src/fkey.c

   1 /*
   2 **
   3 ** The author disclaims copyright to this source code.  In place of
   4 ** a legal notice, here is a blessing:
   5 **
   6 **    May you do good and not evil.
   7 **    May you find forgiveness for yourself and forgive others.
   8 **    May you share freely, never taking more than you give.
   9 **
  10 *************************************************************************
  11 ** This file contains code used by the compiler to add foreign key
  12 ** support to compiled SQL statements.
  13 */
  14 #include "sqliteInt.h"
  15
  16 #ifndef SQLITE_OMIT_FOREIGN_KEY
  17 #ifndef SQLITE_OMIT_TRIGGER
  18
  19 /*
  20 ** Deferred and Immediate FKs
  21 ** --------------------------
  22 **
  23 ** Foreign keys in SQLite come in two flavours: deferred and immediate.
  24 ** If an immediate foreign key constraint is violated,
  25 ** SQLITE_CONSTRAINT_FOREIGNKEY is returned and the current
  26 ** statement transaction rolled back. If a
  27 ** deferred foreign key constraint is violated, no action is taken
  28 ** immediately. However if the application attempts to commit the
  29 ** transaction before fixing the constraint violation, the attempt fails.
  30 **
  31 ** Deferred constraints are implemented using a simple counter associated
  32 ** with the database handle. The counter is set to zero each time a
  33 ** database transaction is opened. Each time a statement is executed
  34 ** that causes a foreign key violation, the counter is incremented. Each
  35 ** time a statement is executed that removes an existing violation from
  36 ** the database, the counter is decremented. When the transaction is
  37 ** committed, the commit fails if the current value of the counter is
  38 ** greater than zero. This scheme has two big drawbacks:
  39 **
  40 **   * When a commit fails due to a deferred foreign key constraint,
  41 **     there is no way to tell which foreign constraint is not satisfied,
  42 **     or which row it is not satisfied for.
  43 **
  44 **   * If the database contains foreign key violations when the
  45 **     transaction is opened, this may cause the mechanism to malfunction.
  46 **
  47 ** Despite these problems, this approach is adopted as it seems simpler
  48 ** than the alternatives.
  49 **
  50 ** INSERT operations:
  51 **
  52 **   I.1) For each FK for which the table is the child table, search
  53 **        the parent table for a match. If none is found increment the
  54 **        constraint counter.
  55 **
  56 **   I.2) For each FK for which the table is the parent table,
  57 **        search the child table for rows that correspond to the new
  58 **        row in the parent table. Decrement the counter for each row
  59 **        found (as the constraint is now satisfied).
  60 **
  61 ** DELETE operations:
  62 **
  63 **   D.1) For each FK for which the table is the child table,
  64 **        search the parent table for a row that corresponds to the
  65 **        deleted row in the child table. If such a row is not found,
  66 **        decrement the counter.
  67 **
  68 **   D.2) For each FK for which the table is the parent table, search
  69 **        the child table for rows that correspond to the deleted row
  70 **        in the parent table. For each found increment the counter.
  71 **
  72 ** UPDATE operations:
  73 **
  74 **   An UPDATE command requires that all 4 steps above are taken, but only
  75 **   for FK constraints for which the affected columns are actually
  76 **   modified (values must be compared at runtime).
  77 **
  78 ** Note that I.1 and D.1 are very similar operations, as are I.2 and D.2.
  79 ** This simplifies the implementation a bit.
  80 **
  81 ** For the purposes of immediate FK constraints, the OR REPLACE conflict
  82 ** resolution is considered to delete rows before the new row is inserted.
  83 ** If a delete caused by OR REPLACE violates an FK constraint, an exception
  84 ** is thrown, even if the FK constraint would be satisfied after the new
  85 ** row is inserted.
  86 **
  87 ** Immediate constraints are usually handled similarly. The only difference
  88 ** is that the counter used is stored as part of each individual statement
  89 ** object (struct Vdbe). If, after the statement has run, its immediate
  90 ** constraint counter is greater than zero,
  91 ** it returns SQLITE_CONSTRAINT_FOREIGNKEY
  92 ** and the statement transaction is rolled back. An exception is an INSERT
  93 ** statement that inserts a single row only (no triggers). In this case,
  94 ** instead of using a counter, an exception is thrown immediately if the
  95 ** INSERT violates a foreign key constraint. This is necessary as such
  96 ** an INSERT does not open a statement transaction.
  97 **
  98 ** TODO: How should dropping a table be handled? How should renaming a
  99 ** table be handled?
 100 **
 101 **
 102 ** Query API Notes
 103 ** ---------------
 104 **
 105 ** Before coding an UPDATE or DELETE row operation, the code-generator
 106 ** for those two operations needs to know whether or not the operation
 107 ** requires any FK processing and, if so, which columns of the original
 108 ** row are required by the FK processing VDBE code (i.e. if FKs were
 109 ** implemented using triggers, which of the old.* columns would be
 110 ** accessed). No information is required by the code-generator before
 111 ** coding an INSERT operation. The functions used by the UPDATE/DELETE
 112 ** generation code to query for this information are:
 113 **
 114 **   sqlite3FkRequired() - Test to see if FK processing is required.
 115 **   sqlite3FkOldmask()  - Query for the set of required old.* columns.
 116 **
 117 **
 118 ** Externally accessible module functions
 119 ** --------------------------------------
 120 **
 121 **   sqlite3FkCheck()    - Check for foreign key violations.
 122 **   sqlite3FkActions()  - Code triggers for ON UPDATE/ON DELETE actions.
 123 **   sqlite3FkDelete()   - Delete an FKey structure.
 124 */
 125
 126 /*
 127 ** VDBE Calling Convention
 128 ** -----------------------
 129 **
 130 ** Example:
 131 **
 132 **   For the following INSERT statement:
 133 **
 134 **     CREATE TABLE t1(a, b INTEGER PRIMARY KEY, c);
 135 **     INSERT INTO t1 VALUES(1, 2, 3.1);
 136 **
 137 **   Register (x):        2    (type integer)
 138 **   Register (x+1):      1    (type integer)
 139 **   Register (x+2):      NULL (type NULL)
 140 **   Register (x+3):      3.1  (type real)
 141 */
 142
 143 /*
 144 ** A foreign key constraint requires that the key columns in the parent
 145 ** table are collectively subject to a UNIQUE or PRIMARY KEY constraint.
 146 ** Given that pParent is the parent table for foreign key constraint pFKey,
 147 ** search the schema for a unique index on the parent key columns.
 148 **
 149 ** If successful, zero is returned. If the parent key is an INTEGER PRIMARY
 150 ** KEY column, then output variable *ppIdx is set to NULL. Otherwise, *ppIdx
 151 ** is set to point to the unique index.
 152 **
 153 ** If the parent key consists of a single column (the foreign key constraint
 154 ** is not a composite foreign key), output variable *paiCol is set to NULL.
 155 ** Otherwise, it is set to point to an allocated array of size N, where
 156 ** N is the number of columns in the parent key. The first element of the
 157 ** array is the index of the child table column that is mapped by the FK
 158 ** constraint to the parent table column stored in the left-most column
 159 ** of index *ppIdx. The second element of the array is the index of the
 160 ** child table column that corresponds to the second left-most column of
 161 ** *ppIdx, and so on.
 162 **
 163 ** If the required index cannot be found, either because:
 164 **
 165 **   1) The named parent key columns do not exist, or
 166 **
 167 **   2) The named parent key columns do exist, but are not subject to a
 168 **      UNIQUE or PRIMARY KEY constraint, or
 169 **
 170 **   3) No parent key columns were provided explicitly as part of the
 171 **      foreign key definition, and the parent table does not have a
 172 **      PRIMARY KEY, or
 173 **
 174 **   4) No parent key columns were provided explicitly as part of the
 175 **      foreign key definition, and the PRIMARY KEY of the parent table
 176 **      consists of a different number of columns to the child key in
 177 **      the child table.
 178 **
 179 ** then non-zero is returned, and a "foreign key mismatch" error loaded
 180 ** into pParse. If an OOM error occurs, non-zero is returned and the
 181 ** pParse->db->mallocFailed flag is set.
 182 */
 183 int sqlite3FkLocateIndex(
 184   Parse *pParse,                  /* Parse context to store any error in */
 185   Table *pParent,                 /* Parent table of FK constraint pFKey */
 186   FKey *pFKey,                    /* Foreign key to find index for */
 187   Index **ppIdx,                  /* OUT: Unique index on parent table */
 188   int **paiCol                    /* OUT: Map of index columns in pFKey */
 189 ){
 190   Index *pIdx = 0;                    /* Value to return via *ppIdx */
 191   int *aiCol = 0;                     /* Value to return via *paiCol */
 192   int nCol = pFKey->nCol;             /* Number of columns in parent key */
 193   char *zKey = pFKey->aCol[0].zCol;   /* Name of left-most parent key column */
 194
 195   /* The caller is responsible for zeroing output parameters. */
 196   assert( ppIdx && *ppIdx==0 );
 197   assert( !paiCol || *paiCol==0 );
 198   assert( pParse );
 199
 200   /* If this is a non-composite (single column) foreign key, check if it
 201   ** maps to the INTEGER PRIMARY KEY of table pParent. If so, leave *ppIdx
 202   ** and *paiCol set to zero and return early.
 203   **
 204   ** Otherwise, for a composite foreign key (more than one column), allocate
 205   ** space for the aiCol array (returned via output parameter *paiCol).
 206   ** Non-composite foreign keys do not require the aiCol array.
 207   */
 208   if( nCol==1 ){
 209     /* The FK maps to the IPK if any of the following are true:
 210     **
 211     **   1) There is an INTEGER PRIMARY KEY column and the FK is implicitly
 212     **      mapped to the primary key of table pParent, or
 213     **   2) The FK is explicitly mapped to a column declared as INTEGER
 214     **      PRIMARY KEY.
 215     */
 216     if( pParent->iPKey>=0 ){
 217       if( !zKey ) return 0;
 218       if( !sqlite3StrICmp(pParent->aCol[pParent->iPKey].zName, zKey) ) return 0;
 219     }
 220   }else if( paiCol ){
 221     assert( nCol>1 );
 222     aiCol = (int *)sqlite3DbMallocRawNN(pParse->db, nCol*sizeof(int));
 223     if( !aiCol ) return 1;
 224     *paiCol = aiCol;
 225   }
 226
 227   for(pIdx=pParent->pIndex; pIdx; pIdx=pIdx->pNext){
 228     if( pIdx->nKeyCol==nCol && IsUniqueIndex(pIdx) && pIdx->pPartIdxWhere==0 ){
 229       /* pIdx is a UNIQUE index (or a PRIMARY KEY) and has the right number
 230       ** of columns. If each indexed column corresponds to a foreign key
 231       ** column of pFKey, then this index is a winner.  */
 232
 233       if( zKey==0 ){
 234         /* If zKey is NULL, then this foreign key is implicitly mapped to
 235         ** the PRIMARY KEY of table pParent. The PRIMARY KEY index may be
 236         ** identified by the test.  */
 237         if( IsPrimaryKeyIndex(pIdx) ){
 238           if( aiCol ){
 239             int i;
 240             for(i=0; i<nCol; i++) aiCol[i] = pFKey->aCol[i].iFrom;
 241           }
 242           break;
 243         }
 244       }else{
 245         /* If zKey is non-NULL, then this foreign key was declared to
 246         ** map to an explicit list of columns in table pParent. Check if this
 247         ** index matches those columns. Also, check that the index uses
 248         ** the default collation sequences for each column. */
 249         int i, j;
 250         for(i=0; i<nCol; i++){
 251           i16 iCol = pIdx->aiColumn[i];     /* Index of column in parent tbl */
 252           const char *zDfltColl;            /* Def. collation for column */
 253           char *zIdxCol;                    /* Name of indexed column */
 254
 255           if( iCol<0 ) break; /* No foreign keys against expression indexes */
 256
 257           /* If the index uses a collation sequence that is different from
 258           ** the default collation sequence for the column, this index is
 259           ** unusable. Bail out early in this case.  */
 260           zDfltColl = pParent->aCol[iCol].zColl;
 261           if( !zDfltColl ) zDfltColl = sqlite3StrBINARY;
 262           if( sqlite3StrICmp(pIdx->azColl[i], zDfltColl) ) break;
 263
 264           zIdxCol = pParent->aCol[iCol].zName;
 265           for(j=0; j<nCol; j++){
 266             if( sqlite3StrICmp(pFKey->aCol[j].zCol, zIdxCol)==0 ){
 267               if( aiCol ) aiCol[i] = pFKey->aCol[j].iFrom;
 268               break;
 269             }
 270           }
 271           if( j==nCol ) break;
 272         }
 273         if( i==nCol ) break;      /* pIdx is usable */
 274       }
 275     }
 276   }
 277
 278   if( !pIdx ){
 279     if( !pParse->disableTriggers ){
 280       sqlite3ErrorMsg(pParse,
 281            "foreign key mismatch - \"%w\" referencing \"%w\"",
 282            pFKey->pFrom->zName, pFKey->zTo);
 283     }
 284     sqlite3DbFree(pParse->db, aiCol);
 285     return 1;
 286   }
 287
 288   *ppIdx = pIdx;
 289   return 0;
 290 }
 291
 292 /*
 293 ** This function is called when a row is inserted into or deleted from the
 294 ** child table of foreign key constraint pFKey. If an SQL UPDATE is executed
 295 ** on the child table of pFKey, this function is invoked twice for each row
 296 ** affected - once to "delete" the old row, and then again to "insert" the
 297 ** new row.
 298 **
 299 ** Each time it is called, this function generates VDBE code to locate the
 300 ** row in the parent table that corresponds to the row being inserted into
 301 ** or deleted from the child table. If the parent row can be found, no
 302 ** special action is taken. Otherwise, if the parent row can *not* be
 303 ** found in the parent table:
 304 **
 305 **   Operation | FK type   | Action taken
 306 **   --------------------------------------------------------------------------
 307 **   INSERT      immediate   Increment the "immediate constraint counter".
 308 **
 309 **   DELETE      immediate   Decrement the "immediate constraint counter".
 310 **
 311 **   INSERT      deferred    Increment the "deferred constraint counter".
 312 **
 313 **   DELETE      deferred    Decrement the "deferred constraint counter".
 314 **
 315 ** These operations are identified in the comment at the top of this file
 316 ** (fkey.c) as "I.1" and "D.1".
 317 */
 318 static void fkLookupParent(
 319   Parse *pParse,        /* Parse context */
 320   int iDb,              /* Index of database housing pTab */
 321   Table *pTab,          /* Parent table of FK pFKey */
 322   Index *pIdx,          /* Unique index on parent key columns in pTab */
 323   FKey *pFKey,          /* Foreign key constraint */
 324   int *aiCol,           /* Map from parent key columns to child table columns */
 325   int regData,          /* Address of array containing child table row */
 326   int nIncr,            /* Increment constraint counter by this */
 327   int isIgnore          /* If true, pretend pTab contains all NULL values */
 328 ){
 329   int i;                                    /* Iterator variable */
 330   Vdbe *v = sqlite3GetVdbe(pParse);         /* Vdbe to add code to */
 331   int iCur = pParse->nTab - 1;              /* Cursor number to use */
 332   int iOk = sqlite3VdbeMakeLabel(v);        /* jump here if parent key found */
 333
 334   sqlite3VdbeVerifyAbortable(v,
 335     (!pFKey->isDeferred
 336       && !(pParse->db->flags & SQLITE_DeferFKs)
 337       && !pParse->pToplevel
 338       && !pParse->isMultiWrite) ? OE_Abort : OE_Ignore);
 339
 340   /* If nIncr is less than zero, then check at runtime if there are any
 341   ** outstanding constraints to resolve. If there are not, there is no need
 342   ** to check if deleting this row resolves any outstanding violations.
 343   **
 344   ** Check if any of the key columns in the child table row are NULL. If
 345   ** any are, then the constraint is considered satisfied. No need to
 346   ** search for a matching row in the parent table.  */
 347   if( nIncr<0 ){
 348     sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, iOk);
 349     VdbeCoverage(v);
 350   }
 351   for(i=0; i<pFKey->nCol; i++){
 352     int iReg = aiCol[i] + regData + 1;
 353     sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iOk); VdbeCoverage(v);
 354   }
 355
 356   if( isIgnore==0 ){
 357     if( pIdx==0 ){
 358       /* If pIdx is NULL, then the parent key is the INTEGER PRIMARY KEY
 359       ** column of the parent table (table pTab).  */
 360       int iMustBeInt;               /* Address of MustBeInt instruction */
 361       int regTemp = sqlite3GetTempReg(pParse);
 362
 363       /* Invoke MustBeInt to coerce the child key value to an integer (i.e.
 364       ** apply the affinity of the parent key). If this fails, then there
 365       ** is no matching parent key. Before using MustBeInt, make a copy of
 366       ** the value. Otherwise, the value inserted into the child key column
 367       ** will have INTEGER affinity applied to it, which may not be correct.  */
 368       sqlite3VdbeAddOp2(v, OP_SCopy, aiCol[0]+1+regData, regTemp);
 369       iMustBeInt = sqlite3VdbeAddOp2(v, OP_MustBeInt, regTemp, 0);
 370       VdbeCoverage(v);
 371
 372       /* If the parent table is the same as the child table, and we are about
 373       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 374       ** then check if the row being inserted matches itself. If so, do not
 375       ** increment the constraint-counter.  */
 376       if( pTab==pFKey->pFrom && nIncr==1 ){
 377         sqlite3VdbeAddOp3(v, OP_Eq, regData, iOk, regTemp); VdbeCoverage(v);
 378         sqlite3VdbeChangeP5(v, SQLITE_NOTNULL);
 379       }
 380
 381       sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);
 382       sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regTemp); VdbeCoverage(v);
 383       sqlite3VdbeGoto(v, iOk);
 384       sqlite3VdbeJumpHere(v, sqlite3VdbeCurrentAddr(v)-2);
 385       sqlite3VdbeJumpHere(v, iMustBeInt);
 386       sqlite3ReleaseTempReg(pParse, regTemp);
 387     }else{
 388       int nCol = pFKey->nCol;
 389       int regTemp = sqlite3GetTempRange(pParse, nCol);
 390       int regRec = sqlite3GetTempReg(pParse);
 391
 392       sqlite3VdbeAddOp3(v, OP_OpenRead, iCur, pIdx->tnum, iDb);
 393       sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
 394       for(i=0; i<nCol; i++){
 395         sqlite3VdbeAddOp2(v, OP_Copy, aiCol[i]+1+regData, regTemp+i);
 396       }
 397
 398       /* If the parent table is the same as the child table, and we are about
 399       ** to increment the constraint-counter (i.e. this is an INSERT operation),
 400       ** then check if the row being inserted matches itself. If so, do not
 401       ** increment the constraint-counter.
 402       **
 403       ** If any of the parent-key values are NULL, then the row cannot match
 404       ** itself. So set JUMPIFNULL to make sure we do the OP_Found if any
 405       ** of the parent-key values are NULL (at this point it is known that
 406       ** none of the child key values are).
 407       */
 408       if( pTab==pFKey->pFrom && nIncr==1 ){
 409         int iJump = sqlite3VdbeCurrentAddr(v) + nCol + 1;
 410         for(i=0; i<nCol; i++){
 411           int iChild = aiCol[i]+1+regData;
 412           int iParent = pIdx->aiColumn[i]+1+regData;
 413           assert( pIdx->aiColumn[i]>=0 );
 414           assert( aiCol[i]!=pTab->iPKey );
 415           if( pIdx->aiColumn[i]==pTab->iPKey ){
 416             /* The parent key is a composite key that includes the IPK column */
 417             iParent = regData;
 418           }
 419           sqlite3VdbeAddOp3(v, OP_Ne, iChild, iJump, iParent); VdbeCoverage(v);
 420           sqlite3VdbeChangeP5(v, SQLITE_JUMPIFNULL);
 421         }
 422         sqlite3VdbeGoto(v, iOk);
 423       }
 424
 425       sqlite3VdbeAddOp4(v, OP_MakeRecord, regTemp, nCol, regRec,
 426                         sqlite3IndexAffinityStr(pParse->db,pIdx), nCol);
 427       sqlite3VdbeAddOp4Int(v, OP_Found, iCur, iOk, regRec, 0); VdbeCoverage(v);
 428
 429       sqlite3ReleaseTempReg(pParse, regRec);
 430       sqlite3ReleaseTempRange(pParse, regTemp, nCol);
 431     }
 432   }
 433
 434   if( !pFKey->isDeferred && !(pParse->db->flags & SQLITE_DeferFKs)
 435    && !pParse->pToplevel
 436    && !pParse->isMultiWrite
 437   ){
 438     /* Special case: If this is an INSERT statement that will insert exactly
 439     ** one row into the table, raise a constraint immediately instead of
 440     ** incrementing a counter. This is necessary as the VM code is being
 441     ** generated for will not open a statement transaction.  */
 442     assert( nIncr==1 );
 443     sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 444         OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 445   }else{
 446     if( nIncr>0 && pFKey->isDeferred==0 ){
 447       sqlite3MayAbort(pParse);
 448     }
 449     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 450   }
 451
 452   sqlite3VdbeResolveLabel(v, iOk);
 453   sqlite3VdbeAddOp1(v, OP_Close, iCur);
 454 }
 455
 456
 457 /*
 458 ** Return an Expr object that refers to a memory register corresponding
 459 ** to column iCol of table pTab.
 460 **
 461 ** regBase is the first of an array of register that contains the data
 462 ** for pTab.  regBase itself holds the rowid.  regBase+1 holds the first
 463 ** column.  regBase+2 holds the second column, and so forth.
 464 */
 465 static Expr *exprTableRegister(
 466   Parse *pParse,     /* Parsing and code generating context */
 467   Table *pTab,       /* The table whose content is at r[regBase]... */
 468   int regBase,       /* Contents of table pTab */
 469   i16 iCol           /* Which column of pTab is desired */
 470 ){
 471   Expr *pExpr;
 472   Column *pCol;
 473   const char *zColl;
 474   sqlite3 *db = pParse->db;
 475
 476   pExpr = sqlite3Expr(db, TK_REGISTER, 0);
 477   if( pExpr ){
 478     if( iCol>=0 && iCol!=pTab->iPKey ){
 479       pCol = &pTab->aCol[iCol];
 480       pExpr->iTable = regBase + iCol + 1;
 481       pExpr->affinity = pCol->affinity;
 482       zColl = pCol->zColl;
 483       if( zColl==0 ) zColl = db->pDfltColl->zName;
 484       pExpr = sqlite3ExprAddCollateString(pParse, pExpr, zColl);
 485     }else{
 486       pExpr->iTable = regBase;
 487       pExpr->affinity = SQLITE_AFF_INTEGER;
 488     }
 489   }
 490   return pExpr;
 491 }
 492
 493 /*
 494 ** Return an Expr object that refers to column iCol of table pTab which
 495 ** has cursor iCur.
 496 */
 497 static Expr *exprTableColumn(
 498   sqlite3 *db,      /* The database connection */
 499   Table *pTab,      /* The table whose column is desired */
 500   int iCursor,      /* The open cursor on the table */
 501   i16 iCol          /* The column that is wanted */
 502 ){
 503   Expr *pExpr = sqlite3Expr(db, TK_COLUMN, 0);
 504   if( pExpr ){
 505     pExpr->pTab = pTab;
 506     pExpr->iTable = iCursor;
 507     pExpr->iColumn = iCol;
 508   }
 509   return pExpr;
 510 }
 511
 512 /*
 513 ** This function is called to generate code executed when a row is deleted
 514 ** from the parent table of foreign key constraint pFKey and, if pFKey is
 515 ** deferred, when a row is inserted into the same table. When generating
 516 ** code for an SQL UPDATE operation, this function may be called twice -
 517 ** once to "delete" the old row and once to "insert" the new row.
 518 **
 519 ** Parameter nIncr is passed -1 when inserting a row (as this may decrease
 520 ** the number of FK violations in the db) or +1 when deleting one (as this
 521 ** may increase the number of FK constraint problems).
 522 **
 523 ** The code generated by this function scans through the rows in the child
 524 ** table that correspond to the parent table row being deleted or inserted.
 525 ** For each child row found, one of the following actions is taken:
 526 **
 527 **   Operation | FK type   | Action taken
 528 **   --------------------------------------------------------------------------
 529 **   DELETE      immediate   Increment the "immediate constraint counter".
 530 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 531 **                           throw a "FOREIGN KEY constraint failed" exception.
 532 **
 533 **   INSERT      immediate   Decrement the "immediate constraint counter".
 534 **
 535 **   DELETE      deferred    Increment the "deferred constraint counter".
 536 **                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
 537 **                           throw a "FOREIGN KEY constraint failed" exception.
 538 **
 539 **   INSERT      deferred    Decrement the "deferred constraint counter".
 540 **
 541 ** These operations are identified in the comment at the top of this file
 542 ** (fkey.c) as "I.2" and "D.2".
 543 */
 544 static void fkScanChildren(
 545   Parse *pParse,                  /* Parse context */
 546   SrcList *pSrc,                  /* The child table to be scanned */
 547   Table *pTab,                    /* The parent table */
 548   Index *pIdx,                    /* Index on parent covering the foreign key */
 549   FKey *pFKey,                    /* The foreign key linking pSrc to pTab */
 550   int *aiCol,                     /* Map from pIdx cols to child table cols */
 551   int regData,                    /* Parent row data starts here */
 552   int nIncr                       /* Amount to increment deferred counter by */
 553 ){
 554   sqlite3 *db = pParse->db;       /* Database handle */
 555   int i;                          /* Iterator variable */
 556   Expr *pWhere = 0;               /* WHERE clause to scan with */
 557   NameContext sNameContext;       /* Context used to resolve WHERE clause */
 558   WhereInfo *pWInfo;              /* Context used by sqlite3WhereXXX() */
 559   int iFkIfZero = 0;              /* Address of OP_FkIfZero */
 560   Vdbe *v = sqlite3GetVdbe(pParse);
 561
 562   assert( pIdx==0 || pIdx->pTable==pTab );
 563   assert( pIdx==0 || pIdx->nKeyCol==pFKey->nCol );
 564   assert( pIdx!=0 || pFKey->nCol==1 );
 565   assert( pIdx!=0 || HasRowid(pTab) );
 566
 567   if( nIncr<0 ){
 568     iFkIfZero = sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, 0);
 569     VdbeCoverage(v);
 570   }
 571
 572   /* Create an Expr object representing an SQL expression like:
 573   **
 574   **   <parent-key1> = <child-key1> AND <parent-key2> = <child-key2> ...
 575   **
 576   ** The collation sequence used for the comparison should be that of
 577   ** the parent key columns. The affinity of the parent key column should
 578   ** be applied to each child key value before the comparison takes place.
 579   */
 580   for(i=0; i<pFKey->nCol; i++){
 581     Expr *pLeft;                  /* Value from parent table row */
 582     Expr *pRight;                 /* Column ref to child table */
 583     Expr *pEq;                    /* Expression (pLeft = pRight) */
 584     i16 iCol;                     /* Index of column in child table */
 585     const char *zCol;             /* Name of column in child table */
 586
 587     iCol = pIdx ? pIdx->aiColumn[i] : -1;
 588     pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 589     iCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
 590     assert( iCol>=0 );
 591     zCol = pFKey->pFrom->aCol[iCol].zName;
 592     pRight = sqlite3Expr(db, TK_ID, zCol);
 593     pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
 594     pWhere = sqlite3ExprAnd(db, pWhere, pEq);
 595   }
 596
 597   /* If the child table is the same as the parent table, then add terms
 598   ** to the WHERE clause that prevent this entry from being scanned.
 599   ** The added WHERE clause terms are like this:
 600   **
 601   **     $current_rowid!=rowid
 602   **     NOT( $current_a==a AND $current_b==b AND ... )
 603   **
 604   ** The first form is used for rowid tables.  The second form is used
 605   ** for WITHOUT ROWID tables.  In the second form, the primary key is
 606   ** (a,b,...)
 607   */
 608   if( pTab==pFKey->pFrom && nIncr>0 ){
 609     Expr *pNe;                    /* Expression (pLeft != pRight) */
 610     Expr *pLeft;                  /* Value from parent table row */
 611     Expr *pRight;                 /* Column ref to child table */
 612     if( HasRowid(pTab) ){
 613       pLeft = exprTableRegister(pParse, pTab, regData, -1);
 614       pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, -1);
 615       pNe = sqlite3PExpr(pParse, TK_NE, pLeft, pRight);
 616     }else{
 617       Expr *pEq, *pAll = 0;
 618       Index *pPk = sqlite3PrimaryKeyIndex(pTab);
 619       assert( pIdx!=0 );
 620       for(i=0; i<pPk->nKeyCol; i++){
 621         i16 iCol = pIdx->aiColumn[i];
 622         assert( iCol>=0 );
 623         pLeft = exprTableRegister(pParse, pTab, regData, iCol);
 624         pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, iCol);
 625         pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
 626         pAll = sqlite3ExprAnd(db, pAll, pEq);
 627       }
 628       pNe = sqlite3PExpr(pParse, TK_NOT, pAll, 0);
 629     }
 630     pWhere = sqlite3ExprAnd(db, pWhere, pNe);
 631   }
 632
 633   /* Resolve the references in the WHERE clause. */
 634   memset(&sNameContext, 0, sizeof(NameContext));
 635   sNameContext.pSrcList = pSrc;
 636   sNameContext.pParse = pParse;
 637   sqlite3ResolveExprNames(&sNameContext, pWhere);
 638
 639   /* Create VDBE to loop through the entries in pSrc that match the WHERE
 640   ** clause. For each row found, increment either the deferred or immediate
 641   ** foreign key constraint counter. */
 642   if( pParse->nErr==0 ){
 643     pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0);
 644     sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
 645     if( pWInfo ){
 646       sqlite3WhereEnd(pWInfo);
 647     }
 648   }
 649
 650   /* Clean up the WHERE clause constructed above. */
 651   sqlite3ExprDelete(db, pWhere);
 652   if( iFkIfZero ){
 653     sqlite3VdbeJumpHere(v, iFkIfZero);
 654   }
 655 }
 656
 657 /*
 658 ** This function returns a linked list of FKey objects (connected by
 659 ** FKey.pNextTo) holding all children of table pTab.  For example,
 660 ** given the following schema:
 661 **
 662 **   CREATE TABLE t1(a PRIMARY KEY);
 663 **   CREATE TABLE t2(b REFERENCES t1(a);
 664 **
 665 ** Calling this function with table "t1" as an argument returns a pointer
 666 ** to the FKey structure representing the foreign key constraint on table
 667 ** "t2". Calling this function with "t2" as the argument would return a
 668 ** NULL pointer (as there are no FK constraints for which t2 is the parent
 669 ** table).
 670 */
 671 FKey *sqlite3FkReferences(Table *pTab){
 672   return (FKey *)sqlite3HashFind(&pTab->pSchema->fkeyHash, pTab->zName);
 673 }
 674
 675 /*
 676 ** The second argument is a Trigger structure allocated by the
 677 ** fkActionTrigger() routine. This function deletes the Trigger structure
 678 ** and all of its sub-components.
 679 **
 680 ** The Trigger structure or any of its sub-components may be allocated from
 681 ** the lookaside buffer belonging to database handle dbMem.
 682 */
 683 static void fkTriggerDelete(sqlite3 *dbMem, Trigger *p){
 684   if( p ){
 685     TriggerStep *pStep = p->step_list;
 686     sqlite3ExprDelete(dbMem, pStep->pWhere);
 687     sqlite3ExprListDelete(dbMem, pStep->pExprList);
 688     sqlite3SelectDelete(dbMem, pStep->pSelect);
 689     sqlite3ExprDelete(dbMem, p->pWhen);
 690     sqlite3DbFree(dbMem, p);
 691   }
 692 }
 693
 694 /*
 695 ** This function is called to generate code that runs when table pTab is
 696 ** being dropped from the database. The SrcList passed as the second argument
 697 ** to this function contains a single entry guaranteed to resolve to
 698 ** table pTab.
 699 **
 700 ** Normally, no code is required. However, if either
 701 **
 702 **   (a) The table is the parent table of a FK constraint, or
 703 **   (b) The table is the child table of a deferred FK constraint and it is
 704 **       determined at runtime that there are outstanding deferred FK
 705 **       constraint violations in the database,
 706 **
 707 ** then the equivalent of "DELETE FROM <tbl>" is executed before dropping
 708 ** the table from the database. Triggers are disabled while running this
 709 ** DELETE, but foreign key actions are not.
 710 */
 711 void sqlite3FkDropTable(Parse *pParse, SrcList *pName, Table *pTab){
 712   sqlite3 *db = pParse->db;
 713   if( (db->flags&SQLITE_ForeignKeys) && !IsVirtual(pTab) && !pTab->pSelect ){
 714     int iSkip = 0;
 715     Vdbe *v = sqlite3GetVdbe(pParse);
 716
 717     assert( v );                  /* VDBE has already been allocated */
 718     if( sqlite3FkReferences(pTab)==0 ){
 719       /* Search for a deferred foreign key constraint for which this table
 720       ** is the child table. If one cannot be found, return without
 721       ** generating any VDBE code. If one can be found, then jump over
 722       ** the entire DELETE if there are no outstanding deferred constraints
 723       ** when this statement is run.  */
 724       FKey *p;
 725       for(p=pTab->pFKey; p; p=p->pNextFrom){
 726         if( p->isDeferred || (db->flags & SQLITE_DeferFKs) ) break;
 727       }
 728       if( !p ) return;
 729       iSkip = sqlite3VdbeMakeLabel(v);
 730       sqlite3VdbeAddOp2(v, OP_FkIfZero, 1, iSkip); VdbeCoverage(v);
 731     }
 732
 733     pParse->disableTriggers = 1;
 734     sqlite3DeleteFrom(pParse, sqlite3SrcListDup(db, pName, 0), 0, 0, 0);
 735     pParse->disableTriggers = 0;
 736
 737     /* If the DELETE has generated immediate foreign key constraint
 738     ** violations, halt the VDBE and return an error at this point, before
 739     ** any modifications to the schema are made. This is because statement
 740     ** transactions are not able to rollback schema changes.
 741     **
 742     ** If the SQLITE_DeferFKs flag is set, then this is not required, as
 743     ** the statement transaction will not be rolled back even if FK
 744     ** constraints are violated.
 745     */
 746     if( (db->flags & SQLITE_DeferFKs)==0 ){
 747       sqlite3VdbeVerifyAbortable(v, OE_Abort);
 748       sqlite3VdbeAddOp2(v, OP_FkIfZero, 0, sqlite3VdbeCurrentAddr(v)+2);
 749       VdbeCoverage(v);
 750       sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
 751           OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
 752     }
 753
 754     if( iSkip ){
 755       sqlite3VdbeResolveLabel(v, iSkip);
 756     }
 757   }
 758 }
 759
 760
 761 /*
 762 ** The second argument points to an FKey object representing a foreign key
 763 ** for which pTab is the child table. An UPDATE statement against pTab
 764 ** is currently being processed. For each column of the table that is
 765 ** actually updated, the corresponding element in the aChange[] array
 766 ** is zero or greater (if a column is unmodified the corresponding element
 767 ** is set to -1). If the rowid column is modified by the UPDATE statement
 768 ** the bChngRowid argument is non-zero.
 769 **
 770 ** This function returns true if any of the columns that are part of the
 771 ** child key for FK constraint *p are modified.
 772 */
 773 static int fkChildIsModified(
 774   Table *pTab,                    /* Table being updated */
 775   FKey *p,                        /* Foreign key for which pTab is the child */
 776   int *aChange,                   /* Array indicating modified columns */
 777   int bChngRowid                  /* True if rowid is modified by this update */
 778 ){
 779   int i;
 780   for(i=0; i<p->nCol; i++){
 781     int iChildKey = p->aCol[i].iFrom;
 782     if( aChange[iChildKey]>=0 ) return 1;
 783     if( iChildKey==pTab->iPKey && bChngRowid ) return 1;
 784   }
 785   return 0;
 786 }
 787
 788 /*
 789 ** The second argument points to an FKey object representing a foreign key
 790 ** for which pTab is the parent table. An UPDATE statement against pTab
 791 ** is currently being processed. For each column of the table that is
 792 ** actually updated, the corresponding element in the aChange[] array
 793 ** is zero or greater (if a column is unmodified the corresponding element
 794 ** is set to -1). If the rowid column is modified by the UPDATE statement
 795 ** the bChngRowid argument is non-zero.
 796 **
 797 ** This function returns true if any of the columns that are part of the
 798 ** parent key for FK constraint *p are modified.
 799 */
 800 static int fkParentIsModified(
 801   Table *pTab,
 802   FKey *p,
 803   int *aChange,
 804   int bChngRowid
 805 ){
 806   int i;
 807   for(i=0; i<p->nCol; i++){
 808     char *zKey = p->aCol[i].zCol;
 809     int iKey;
 810     for(iKey=0; iKey<pTab->nCol; iKey++){
 811       if( aChange[iKey]>=0 || (iKey==pTab->iPKey && bChngRowid) ){
 812         Column *pCol = &pTab->aCol[iKey];
 813         if( zKey ){
 814           if( 0==sqlite3StrICmp(pCol->zName, zKey) ) return 1;
 815         }else if( pCol->colFlags & COLFLAG_PRIMKEY ){
 816           return 1;
 817         }
 818       }
 819     }
 820   }
 821   return 0;
 822 }
 823
 824 /*
 825 ** Return true if the parser passed as the first argument is being
 826 ** used to code a trigger that is really a "SET NULL" action belonging
 827 ** to trigger pFKey.
 828 */
 829 static int isSetNullAction(Parse *pParse, FKey *pFKey){
 830   Parse *pTop = sqlite3ParseToplevel(pParse);
 831   if( pTop->pTriggerPrg ){
 832     Trigger *p = pTop->pTriggerPrg->pTrigger;
 833     if( (p==pFKey->apTrigger[0] && pFKey->aAction[0]==OE_SetNull)
 834      || (p==pFKey->apTrigger[1] && pFKey->aAction[1]==OE_SetNull)
 835     ){
 836       return 1;
 837     }
 838   }
 839   return 0;
 840 }
 841
 842 /*
 843 ** This function is called when inserting, deleting or updating a row of
 844 ** table pTab to generate VDBE code to perform foreign key constraint
 845 ** processing for the operation.
 846 **
 847 ** For a DELETE operation, parameter regOld is passed the index of the
 848 ** first register in an array of (pTab->nCol+1) registers containing the
 849 ** rowid of the row being deleted, followed by each of the column values
 850 ** of the row being deleted, from left to right. Parameter regNew is passed
 851 ** zero in this case.
 852 **
 853 ** For an INSERT operation, regOld is passed zero and regNew is passed the
 854 ** first register of an array of (pTab->nCol+1) registers containing the new
 855 ** row data.
 856 **
 857 ** For an UPDATE operation, this function is called twice. Once before
 858 ** the original record is deleted from the table using the calling convention
 859 ** described for DELETE. Then again after the original record is deleted
 860 ** but before the new record is inserted using the INSERT convention.
 861 */
 862 void sqlite3FkCheck(
 863   Parse *pParse,                  /* Parse context */
 864   Table *pTab,                    /* Row is being deleted from this table */
 865   int regOld,                     /* Previous row data is stored here */
 866   int regNew,                     /* New row data is stored here */
 867   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
 868   int bChngRowid                  /* True if rowid is UPDATEd */
 869 ){
 870   sqlite3 *db = pParse->db;       /* Database handle */
 871   FKey *pFKey;                    /* Used to iterate through FKs */
 872   int iDb;                        /* Index of database containing pTab */
 873   const char *zDb;                /* Name of database containing pTab */
 874   int isIgnoreErrors = pParse->disableTriggers;
 875
 876   /* Exactly one of regOld and regNew should be non-zero. */
 877   assert( (regOld==0)!=(regNew==0) );
 878
 879   /* If foreign-keys are disabled, this function is a no-op. */
 880   if( (db->flags&SQLITE_ForeignKeys)==0 ) return;
 881
 882   iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
 883   zDb = db->aDb[iDb].zDbSName;
 884
 885   /* Loop through all the foreign key constraints for which pTab is the
 886   ** child table (the table that the foreign key definition is part of).  */
 887   for(pFKey=pTab->pFKey; pFKey; pFKey=pFKey->pNextFrom){
 888     Table *pTo;                   /* Parent table of foreign key pFKey */
 889     Index *pIdx = 0;              /* Index on key columns in pTo */
 890     int *aiFree = 0;
 891     int *aiCol;
 892     int iCol;
 893     int i;
 894     int bIgnore = 0;
 895
 896     if( aChange
 897      && sqlite3_stricmp(pTab->zName, pFKey->zTo)!=0
 898      && fkChildIsModified(pTab, pFKey, aChange, bChngRowid)==0
 899     ){
 900       continue;
 901     }
 902
 903     /* Find the parent table of this foreign key. Also find a unique index
 904     ** on the parent key columns in the parent table. If either of these
 905     ** schema items cannot be located, set an error in pParse and return
 906     ** early.  */
 907     if( pParse->disableTriggers ){
 908       pTo = sqlite3FindTable(db, pFKey->zTo, zDb);
 909     }else{
 910       pTo = sqlite3LocateTable(pParse, 0, pFKey->zTo, zDb);
 911     }
 912     if( !pTo || sqlite3FkLocateIndex(pParse, pTo, pFKey, &pIdx, &aiFree) ){
 913       assert( isIgnoreErrors==0 || (regOld!=0 && regNew==0) );
 914       if( !isIgnoreErrors || db->mallocFailed ) return;
 915       if( pTo==0 ){
 916         /* If isIgnoreErrors is true, then a table is being dropped. In this
 917         ** case SQLite runs a "DELETE FROM xxx" on the table being dropped
 918         ** before actually dropping it in order to check FK constraints.
 919         ** If the parent table of an FK constraint on the current table is
 920         ** missing, behave as if it is empty. i.e. decrement the relevant
 921         ** FK counter for each row of the current table with non-NULL keys.
 922         */
 923         Vdbe *v = sqlite3GetVdbe(pParse);
 924         int iJump = sqlite3VdbeCurrentAddr(v) + pFKey->nCol + 1;
 925         for(i=0; i<pFKey->nCol; i++){
 926           int iReg = pFKey->aCol[i].iFrom + regOld + 1;
 927           sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iJump); VdbeCoverage(v);
 928         }
 929         sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, -1);
 930       }
 931       continue;
 932     }
 933     assert( pFKey->nCol==1 || (aiFree && pIdx) );
 934
 935     if( aiFree ){
 936       aiCol = aiFree;
 937     }else{
 938       iCol = pFKey->aCol[0].iFrom;
 939       aiCol = &iCol;
 940     }
 941     for(i=0; i<pFKey->nCol; i++){
 942       if( aiCol[i]==pTab->iPKey ){
 943         aiCol[i] = -1;
 944       }
 945       assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
 946 #ifndef SQLITE_OMIT_AUTHORIZATION
 947       /* Request permission to read the parent key columns. If the
 948       ** authorization callback returns SQLITE_IGNORE, behave as if any
 949       ** values read from the parent table are NULL. */
 950       if( db->xAuth ){
 951         int rcauth;
 952         char *zCol = pTo->aCol[pIdx ? pIdx->aiColumn[i] : pTo->iPKey].zName;
 953         rcauth = sqlite3AuthReadCol(pParse, pTo->zName, zCol, iDb);
 954         bIgnore = (rcauth==SQLITE_IGNORE);
 955       }
 956 #endif
 957     }
 958
 959     /* Take a shared-cache advisory read-lock on the parent table. Allocate
 960     ** a cursor to use to search the unique index on the parent key columns
 961     ** in the parent table.  */
 962     sqlite3TableLock(pParse, iDb, pTo->tnum, 0, pTo->zName);
 963     pParse->nTab++;
 964
 965     if( regOld!=0 ){
 966       /* A row is being removed from the child table. Search for the parent.
 967       ** If the parent does not exist, removing the child row resolves an
 968       ** outstanding foreign key constraint violation. */
 969       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regOld, -1, bIgnore);
 970     }
 971     if( regNew!=0 && !isSetNullAction(pParse, pFKey) ){
 972       /* A row is being added to the child table. If a parent row cannot
 973       ** be found, adding the child row has violated the FK constraint.
 974       **
 975       ** If this operation is being performed as part of a trigger program
 976       ** that is actually a "SET NULL" action belonging to this very
 977       ** foreign key, then omit this scan altogether. As all child key
 978       ** values are guaranteed to be NULL, it is not possible for adding
 979       ** this row to cause an FK violation.  */
 980       fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regNew, +1, bIgnore);
 981     }
 982
 983     sqlite3DbFree(db, aiFree);
 984   }
 985
 986   /* Loop through all the foreign key constraints that refer to this table.
 987   ** (the "child" constraints) */
 988   for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
 989     Index *pIdx = 0;              /* Foreign key index for pFKey */
 990     SrcList *pSrc;
 991     int *aiCol = 0;
 992
 993     if( aChange && fkParentIsModified(pTab, pFKey, aChange, bChngRowid)==0 ){
 994       continue;
 995     }
 996
 997     if( !pFKey->isDeferred && !(db->flags & SQLITE_DeferFKs)
 998      && !pParse->pToplevel && !pParse->isMultiWrite
 999     ){
1000       assert( regOld==0 && regNew!=0 );
1001       /* Inserting a single row into a parent table cannot cause (or fix)
1002       ** an immediate foreign key violation. So do nothing in this case.  */
1003       continue;
1004     }
1005
1006     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ){
1007       if( !isIgnoreErrors || db->mallocFailed ) return;
1008       continue;
1009     }
1010     assert( aiCol || pFKey->nCol==1 );
1011
1012     /* Create a SrcList structure containing the child table.  We need the
1013     ** child table as a SrcList for sqlite3WhereBegin() */
1014     pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
1015     if( pSrc ){
1016       struct SrcList_item *pItem = pSrc->a;
1017       pItem->pTab = pFKey->pFrom;
1018       pItem->zName = pFKey->pFrom->zName;
1019       pItem->pTab->nTabRef++;
1020       pItem->iCursor = pParse->nTab++;
1021
1022       if( regNew!=0 ){
1023         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regNew, -1);
1024       }
1025       if( regOld!=0 ){
1026         int eAction = pFKey->aAction[aChange!=0];
1027         fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regOld, 1);
1028         /* If this is a deferred FK constraint, or a CASCADE or SET NULL
1029         ** action applies, then any foreign key violations caused by
1030         ** removing the parent key will be rectified by the action trigger.
1031         ** So do not set the "may-abort" flag in this case.
1032         **
1033         ** Note 1: If the FK is declared "ON UPDATE CASCADE", then the
1034         ** may-abort flag will eventually be set on this statement anyway
1035         ** (when this function is called as part of processing the UPDATE
1036         ** within the action trigger).
1037         **
1038         ** Note 2: At first glance it may seem like SQLite could simply omit
1039         ** all OP_FkCounter related scans when either CASCADE or SET NULL
1040         ** applies. The trouble starts if the CASCADE or SET NULL action
1041         ** trigger causes other triggers or action rules attached to the
1042         ** child table to fire. In these cases the fk constraint counters
1043         ** might be set incorrectly if any OP_FkCounter related scans are
1044         ** omitted.  */
1045         if( !pFKey->isDeferred && eAction!=OE_Cascade && eAction!=OE_SetNull ){
1046           sqlite3MayAbort(pParse);
1047         }
1048       }
1049       pItem->zName = 0;
1050       sqlite3SrcListDelete(db, pSrc);
1051     }
1052     sqlite3DbFree(db, aiCol);
1053   }
1054 }
1055
1056 #define COLUMN_MASK(x) (((x)>31) ? 0xffffffff : ((u32)1<<(x)))
1057
1058 /*
1059 ** This function is called before generating code to update or delete a
1060 ** row contained in table pTab.
1061 */
1062 u32 sqlite3FkOldmask(
1063   Parse *pParse,                  /* Parse context */
1064   Table *pTab                     /* Table being modified */
1065 ){
1066   u32 mask = 0;
1067   if( pParse->db->flags&SQLITE_ForeignKeys ){
1068     FKey *p;
1069     int i;
1070     for(p=pTab->pFKey; p; p=p->pNextFrom){
1071       for(i=0; i<p->nCol; i++) mask |= COLUMN_MASK(p->aCol[i].iFrom);
1072     }
1073     for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1074       Index *pIdx = 0;
1075       sqlite3FkLocateIndex(pParse, pTab, p, &pIdx, 0);
1076       if( pIdx ){
1077         for(i=0; i<pIdx->nKeyCol; i++){
1078           assert( pIdx->aiColumn[i]>=0 );
1079           mask |= COLUMN_MASK(pIdx->aiColumn[i]);
1080         }
1081       }
1082     }
1083   }
1084   return mask;
1085 }
1086
1087
1088 /*
1089 ** This function is called before generating code to update or delete a
1090 ** row contained in table pTab. If the operation is a DELETE, then
1091 ** parameter aChange is passed a NULL value. For an UPDATE, aChange points
1092 ** to an array of size N, where N is the number of columns in table pTab.
1093 ** If the i'th column is not modified by the UPDATE, then the corresponding
1094 ** entry in the aChange[] array is set to -1. If the column is modified,
1095 ** the value is 0 or greater. Parameter chngRowid is set to true if the
1096 ** UPDATE statement modifies the rowid fields of the table.
1097 **
1098 ** If any foreign key processing will be required, this function returns
1099 ** non-zero. If there is no foreign key related processing, this function
1100 ** returns zero.
1101 **
1102 ** For an UPDATE, this function returns 2 if:
1103 **
1104 **   * There are any FKs for which pTab is the child and the parent table, or
1105 **   * the UPDATE modifies one or more parent keys for which the action is
1106 **     not "NO ACTION" (i.e. is CASCADE, SET DEFAULT or SET NULL).
1107 **
1108 ** Or, assuming some other foreign key processing is required, 1.
1109 */
1110 int sqlite3FkRequired(
1111   Parse *pParse,                  /* Parse context */
1112   Table *pTab,                    /* Table being modified */
1113   int *aChange,                   /* Non-NULL for UPDATE operations */
1114   int chngRowid                   /* True for UPDATE that affects rowid */
1115 ){
1116   int eRet = 0;
1117   if( pParse->db->flags&SQLITE_ForeignKeys ){
1118     if( !aChange ){
1119       /* A DELETE operation. Foreign key processing is required if the
1120       ** table in question is either the child or parent table for any
1121       ** foreign key constraint.  */
1122       eRet = (sqlite3FkReferences(pTab) || pTab->pFKey);
1123     }else{
1124       /* This is an UPDATE. Foreign key processing is only required if the
1125       ** operation modifies one or more child or parent key columns. */
1126       FKey *p;
1127
1128       /* Check if any child key columns are being modified. */
1129       for(p=pTab->pFKey; p; p=p->pNextFrom){
1130         if( 0==sqlite3_stricmp(pTab->zName, p->zTo) ) return 2;
1131         if( fkChildIsModified(pTab, p, aChange, chngRowid) ){
1132           eRet = 1;
1133         }
1134       }
1135
1136       /* Check if any parent key columns are being modified. */
1137       for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
1138         if( fkParentIsModified(pTab, p, aChange, chngRowid) ){
1139           if( p->aAction[1]!=OE_None ) return 2;
1140           eRet = 1;
1141         }
1142       }
1143     }
1144   }
1145   return eRet;
1146 }
1147
1148 /*
1149 ** This function is called when an UPDATE or DELETE operation is being
1150 ** compiled on table pTab, which is the parent table of foreign-key pFKey.
1151 ** If the current operation is an UPDATE, then the pChanges parameter is
1152 ** passed a pointer to the list of columns being modified. If it is a
1153 ** DELETE, pChanges is passed a NULL pointer.
1154 **
1155 ** It returns a pointer to a Trigger structure containing a trigger
1156 ** equivalent to the ON UPDATE or ON DELETE action specified by pFKey.
1157 ** If the action is "NO ACTION" or "RESTRICT", then a NULL pointer is
1158 ** returned (these actions require no special handling by the triggers
1159 ** sub-system, code for them is created by fkScanChildren()).
1160 **
1161 ** For example, if pFKey is the foreign key and pTab is table "p" in
1162 ** the following schema:
1163 **
1164 **   CREATE TABLE p(pk PRIMARY KEY);
1165 **   CREATE TABLE c(ck REFERENCES p ON DELETE CASCADE);
1166 **
1167 ** then the returned trigger structure is equivalent to:
1168 **
1169 **   CREATE TRIGGER ... DELETE ON p BEGIN
1170 **     DELETE FROM c WHERE ck = old.pk;
1171 **   END;
1172 **
1173 ** The returned pointer is cached as part of the foreign key object. It
1174 ** is eventually freed along with the rest of the foreign key object by
1175 ** sqlite3FkDelete().
1176 */
1177 static Trigger *fkActionTrigger(
1178   Parse *pParse,                  /* Parse context */
1179   Table *pTab,                    /* Table being updated or deleted from */
1180   FKey *pFKey,                    /* Foreign key to get action for */
1181   ExprList *pChanges              /* Change-list for UPDATE, NULL for DELETE */
1182 ){
1183   sqlite3 *db = pParse->db;       /* Database handle */
1184   int action;                     /* One of OE_None, OE_Cascade etc. */
1185   Trigger *pTrigger;              /* Trigger definition to return */
1186   int iAction = (pChanges!=0);    /* 1 for UPDATE, 0 for DELETE */
1187
1188   action = pFKey->aAction[iAction];
1189   if( action==OE_Restrict && (db->flags & SQLITE_DeferFKs) ){
1190     return 0;
1191   }
1192   pTrigger = pFKey->apTrigger[iAction];
1193
1194   if( action!=OE_None && !pTrigger ){
1195     char const *zFrom;            /* Name of child table */
1196     int nFrom;                    /* Length in bytes of zFrom */
1197     Index *pIdx = 0;              /* Parent key index for this FK */
1198     int *aiCol = 0;               /* child table cols -> parent key cols */
1199     TriggerStep *pStep = 0;        /* First (only) step of trigger program */
1200     Expr *pWhere = 0;             /* WHERE clause of trigger step */
1201     ExprList *pList = 0;          /* Changes list if ON UPDATE CASCADE */
1202     Select *pSelect = 0;          /* If RESTRICT, "SELECT RAISE(...)" */
1203     int i;                        /* Iterator variable */
1204     Expr *pWhen = 0;              /* WHEN clause for the trigger */
1205
1206     if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ) return 0;
1207     assert( aiCol || pFKey->nCol==1 );
1208
1209     for(i=0; i<pFKey->nCol; i++){
1210       Token tOld = { "old", 3 };  /* Literal "old" token */
1211       Token tNew = { "new", 3 };  /* Literal "new" token */
1212       Token tFromCol;             /* Name of column in child table */
1213       Token tToCol;               /* Name of column in parent table */
1214       int iFromCol;               /* Idx of column in child table */
1215       Expr *pEq;                  /* tFromCol = OLD.tToCol */
1216
1217       iFromCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
1218       assert( iFromCol>=0 );
1219       assert( pIdx!=0 || (pTab->iPKey>=0 && pTab->iPKey<pTab->nCol) );
1220       assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
1221       sqlite3TokenInit(&tToCol,
1222                    pTab->aCol[pIdx ? pIdx->aiColumn[i] : pTab->iPKey].zName);
1223       sqlite3TokenInit(&tFromCol, pFKey->pFrom->aCol[iFromCol].zName);
1224
1225       /* Create the expression "OLD.zToCol = zFromCol". It is important
1226       ** that the "OLD.zToCol" term is on the LHS of the = operator, so
1227       ** that the affinity and collation sequence associated with the
1228       ** parent table are used for the comparison. */
1229       pEq = sqlite3PExpr(pParse, TK_EQ,
1230           sqlite3PExpr(pParse, TK_DOT,
1231             sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
1232             sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
1233           sqlite3ExprAlloc(db, TK_ID, &tFromCol, 0)
1234       );
1235       pWhere = sqlite3ExprAnd(db, pWhere, pEq);
1236
1237       /* For ON UPDATE, construct the next term of the WHEN clause.
1238       ** The final WHEN clause will be like this:
1239       **
1240       **    WHEN NOT(old.col1 IS new.col1 AND ... AND old.colN IS new.colN)
1241       */
1242       if( pChanges ){
1243         pEq = sqlite3PExpr(pParse, TK_IS,
1244             sqlite3PExpr(pParse, TK_DOT,
1245               sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
1246               sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
1247             sqlite3PExpr(pParse, TK_DOT,
1248               sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
1249               sqlite3ExprAlloc(db, TK_ID, &tToCol, 0))
1250             );
1251         pWhen = sqlite3ExprAnd(db, pWhen, pEq);
1252       }
1253
1254       if( action!=OE_Restrict && (action!=OE_Cascade || pChanges) ){
1255         Expr *pNew;
1256         if( action==OE_Cascade ){
1257           pNew = sqlite3PExpr(pParse, TK_DOT,
1258             sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
1259             sqlite3ExprAlloc(db, TK_ID, &tToCol, 0));
1260         }else if( action==OE_SetDflt ){
1261           Expr *pDflt = pFKey->pFrom->aCol[iFromCol].pDflt;
1262           if( pDflt ){
1263             pNew = sqlite3ExprDup(db, pDflt, 0);
1264           }else{
1265             pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
1266           }
1267         }else{
1268           pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
1269         }
1270         pList = sqlite3ExprListAppend(pParse, pList, pNew);
1271         sqlite3ExprListSetName(pParse, pList, &tFromCol, 0);
1272       }
1273     }
1274     sqlite3DbFree(db, aiCol);
1275
1276     zFrom = pFKey->pFrom->zName;
1277     nFrom = sqlite3Strlen30(zFrom);
1278
1279     if( action==OE_Restrict ){
1280       Token tFrom;
1281       Expr *pRaise;
1282
1283       tFrom.z = zFrom;
1284       tFrom.n = nFrom;
1285       pRaise = sqlite3Expr(db, TK_RAISE, "FOREIGN KEY constraint failed");
1286       if( pRaise ){
1287         pRaise->affinity = OE_Abort;
1288       }
1289       pSelect = sqlite3SelectNew(pParse,
1290           sqlite3ExprListAppend(pParse, 0, pRaise),
1291           sqlite3SrcListAppend(db, 0, &tFrom, 0),
1292           pWhere,
1293           0, 0, 0, 0, 0
1294       );
1295       pWhere = 0;
1296     }
1297
1298     /* Disable lookaside memory allocation */
1299     db->lookaside.bDisable++;
1300
1301     pTrigger = (Trigger *)sqlite3DbMallocZero(db,
1302         sizeof(Trigger) +         /* struct Trigger */
1303         sizeof(TriggerStep) +     /* Single step in trigger program */
1304         nFrom + 1                 /* Space for pStep->zTarget */
1305     );
1306     if( pTrigger ){
1307       pStep = pTrigger->step_list = (TriggerStep *)&pTrigger[1];
1308       pStep->zTarget = (char *)&pStep[1];
1309       memcpy((char *)pStep->zTarget, zFrom, nFrom);
1310
1311       pStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
1312       pStep->pExprList = sqlite3ExprListDup(db, pList, EXPRDUP_REDUCE);
1313       pStep->pSelect = sqlite3SelectDup(db, pSelect, EXPRDUP_REDUCE);
1314       if( pWhen ){
1315         pWhen = sqlite3PExpr(pParse, TK_NOT, pWhen, 0);
1316         pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
1317       }
1318     }
1319
1320     /* Re-enable the lookaside buffer, if it was disabled earlier. */
1321     db->lookaside.bDisable--;
1322
1323     sqlite3ExprDelete(db, pWhere);
1324     sqlite3ExprDelete(db, pWhen);
1325     sqlite3ExprListDelete(db, pList);
1326     sqlite3SelectDelete(db, pSelect);
1327     if( db->mallocFailed==1 ){
1328       fkTriggerDelete(db, pTrigger);
1329       return 0;
1330     }
1331     assert( pStep!=0 );
1332
1333     switch( action ){
1334       case OE_Restrict:
1335         pStep->op = TK_SELECT;
1336         break;
1337       case OE_Cascade:
1338         if( !pChanges ){
1339           pStep->op = TK_DELETE;
1340           break;
1341         }
1342       default:
1343         pStep->op = TK_UPDATE;
1344     }
1345     pStep->pTrig = pTrigger;
1346     pTrigger->pSchema = pTab->pSchema;
1347     pTrigger->pTabSchema = pTab->pSchema;
1348     pFKey->apTrigger[iAction] = pTrigger;
1349     pTrigger->op = (pChanges ? TK_UPDATE : TK_DELETE);
1350   }
1351
1352   return pTrigger;
1353 }
1354
1355 /*
1356 ** This function is called when deleting or updating a row to implement
1357 ** any required CASCADE, SET NULL or SET DEFAULT actions.
1358 */
1359 void sqlite3FkActions(
1360   Parse *pParse,                  /* Parse context */
1361   Table *pTab,                    /* Table being updated or deleted from */
1362   ExprList *pChanges,             /* Change-list for UPDATE, NULL for DELETE */
1363   int regOld,                     /* Address of array containing old row */
1364   int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
1365   int bChngRowid                  /* True if rowid is UPDATEd */
1366 ){
1367   /* If foreign-key support is enabled, iterate through all FKs that
1368   ** refer to table pTab. If there is an action associated with the FK
1369   ** for this operation (either update or delete), invoke the associated
1370   ** trigger sub-program.  */
1371   if( pParse->db->flags&SQLITE_ForeignKeys ){
1372     FKey *pFKey;                  /* Iterator variable */
1373     for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
1374       if( aChange==0 || fkParentIsModified(pTab, pFKey, aChange, bChngRowid) ){
1375         Trigger *pAct = fkActionTrigger(pParse, pTab, pFKey, pChanges);
1376         if( pAct ){
1377           sqlite3CodeRowTriggerDirect(pParse, pAct, pTab, regOld, OE_Abort, 0);
1378         }
1379       }
1380     }
1381   }
1382 }
1383
1384 #endif /* ifndef SQLITE_OMIT_TRIGGER */
1385
1386 /*
1387 ** Free all memory associated with foreign key definitions attached to
1388 ** table pTab. Remove the deleted foreign keys from the Schema.fkeyHash
1389 ** hash table.
1390 */
1391 void sqlite3FkDelete(sqlite3 *db, Table *pTab){
1392   FKey *pFKey;                    /* Iterator variable */
1393   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
1394
1395   assert( db==0 || IsVirtual(pTab)
1396          || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
1397   for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
1398
1399     /* Remove the FK from the fkeyHash hash table. */
1400     if( !db || db->pnBytesFreed==0 ){
1401       if( pFKey->pPrevTo ){
1402         pFKey->pPrevTo->pNextTo = pFKey->pNextTo;
1403       }else{
1404         void *p = (void *)pFKey->pNextTo;
1405         const char *z = (p ? pFKey->pNextTo->zTo : pFKey->zTo);
1406         sqlite3HashInsert(&pTab->pSchema->fkeyHash, z, p);
1407       }
1408       if( pFKey->pNextTo ){
1409         pFKey->pNextTo->pPrevTo = pFKey->pPrevTo;
1410       }
1411     }
1412
1413     /* EV: R-30323-21917 Each foreign key constraint in SQLite is
1414     ** classified as either immediate or deferred.
1415     */
1416     assert( pFKey->isDeferred==0 || pFKey->isDeferred==1 );
1417
1418     /* Delete any triggers created to implement actions for this FK. */
1419 #ifndef SQLITE_OMIT_TRIGGER
1420     fkTriggerDelete(db, pFKey->apTrigger[0]);
1421     fkTriggerDelete(db, pFKey->apTrigger[1]);
1422 #endif
1423
1424     pNext = pFKey->pNextFrom;
1425     sqlite3DbFree(db, pFKey);
1426   }
1427 }
1428 #endif /* ifndef SQLITE_OMIT_FOREIGN_KEY */