src/walker.c

   1 /*
   2 ** 2008 August 16
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 ** This file contains routines used for walking the parser tree for
  13 ** an SQL statement.
  14 */
  15 #include "sqliteInt.h"
  16 #include <stdlib.h>
  17 #include <string.h>
  18
  19
  20 /*
  21 ** Walk an expression tree.  Invoke the callback once for each node
  22 ** of the expression, while descending.  (In other words, the callback
  23 ** is invoked before visiting children.)
  24 **
  25 ** The return value from the callback should be one of the WRC_*
  26 ** constants to specify how to proceed with the walk.
  27 **
  28 **    WRC_Continue      Continue descending down the tree.
  29 **
  30 **    WRC_Prune         Do not descend into child nodes, but allow
  31 **                      the walk to continue with sibling nodes.
  32 **
  33 **    WRC_Abort         Do no more callbacks.  Unwind the stack and
  34 **                      return from the top-level walk call.
  35 **
  36 ** The return value from this routine is WRC_Abort to abandon the tree walk
  37 ** and WRC_Continue to continue.
  38 */
  39 static SQLITE_NOINLINE int walkExpr(Walker *pWalker, Expr *pExpr){
  40   int rc;
  41   testcase( ExprHasProperty(pExpr, EP_TokenOnly) );
  42   testcase( ExprHasProperty(pExpr, EP_Reduced) );
  43   while(1){
  44     rc = pWalker->xExprCallback(pWalker, pExpr);
  45     if( rc ) return rc & WRC_Abort;
  46     if( !ExprHasProperty(pExpr,(EP_TokenOnly|EP_Leaf)) ){
  47       if( pExpr->pLeft && walkExpr(pWalker, pExpr->pLeft) ) return WRC_Abort;
  48        assert( pExpr->x.pList==0 || pExpr->pRight==0 );
  49       if( pExpr->pRight ){
  50         pExpr = pExpr->pRight;
  51         continue;
  52       }else if( ExprHasProperty(pExpr, EP_xIsSelect) ){
  53         if( sqlite3WalkSelect(pWalker, pExpr->x.pSelect) ) return WRC_Abort;
  54       }else if( pExpr->x.pList ){
  55         if( sqlite3WalkExprList(pWalker, pExpr->x.pList) ) return WRC_Abort;
  56       }
  57     }
  58     break;
  59   }
  60   return WRC_Continue;
  61 }
  62 int sqlite3WalkExpr(Walker *pWalker, Expr *pExpr){
  63   return pExpr ? walkExpr(pWalker,pExpr) : WRC_Continue;
  64 }
  65
  66 /*
  67 ** Call sqlite3WalkExpr() for every expression in list p or until
  68 ** an abort request is seen.
  69 */
  70 int sqlite3WalkExprList(Walker *pWalker, ExprList *p){
  71   int i;
  72   struct ExprList_item *pItem;
  73   if( p ){
  74     for(i=p->nExpr, pItem=p->a; i>0; i--, pItem++){
  75       if( sqlite3WalkExpr(pWalker, pItem->pExpr) ) return WRC_Abort;
  76     }
  77   }
  78   return WRC_Continue;
  79 }
  80
  81 /*
  82 ** Walk all expressions associated with SELECT statement p.  Do
  83 ** not invoke the SELECT callback on p, but do (of course) invoke
  84 ** any expr callbacks and SELECT callbacks that come from subqueries.
  85 ** Return WRC_Abort or WRC_Continue.
  86 */
  87 int sqlite3WalkSelectExpr(Walker *pWalker, Select *p){
  88   if( sqlite3WalkExprList(pWalker, p->pEList) ) return WRC_Abort;
  89   if( sqlite3WalkExpr(pWalker, p->pWhere) ) return WRC_Abort;
  90   if( sqlite3WalkExprList(pWalker, p->pGroupBy) ) return WRC_Abort;
  91   if( sqlite3WalkExpr(pWalker, p->pHaving) ) return WRC_Abort;
  92   if( sqlite3WalkExprList(pWalker, p->pOrderBy) ) return WRC_Abort;
  93   if( sqlite3WalkExpr(pWalker, p->pLimit) ) return WRC_Abort;
  94   if( sqlite3WalkExpr(pWalker, p->pOffset) ) return WRC_Abort;
  95   return WRC_Continue;
  96 }
  97
  98 /*
  99 ** Walk the parse trees associated with all subqueries in the
 100 ** FROM clause of SELECT statement p.  Do not invoke the select
 101 ** callback on p, but do invoke it on each FROM clause subquery
 102 ** and on any subqueries further down in the tree.  Return
 103 ** WRC_Abort or WRC_Continue;
 104 */
 105 int sqlite3WalkSelectFrom(Walker *pWalker, Select *p){
 106   SrcList *pSrc;
 107   int i;
 108   struct SrcList_item *pItem;
 109
 110   pSrc = p->pSrc;
 111   if( ALWAYS(pSrc) ){
 112     for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){
 113       if( pItem->pSelect && sqlite3WalkSelect(pWalker, pItem->pSelect) ){
 114         return WRC_Abort;
 115       }
 116       if( pItem->fg.isTabFunc
 117        && sqlite3WalkExprList(pWalker, pItem->u1.pFuncArg)
 118       ){
 119         return WRC_Abort;
 120       }
 121     }
 122   }
 123   return WRC_Continue;
 124 }
 125
 126 /*
 127 ** Call sqlite3WalkExpr() for every expression in Select statement p.
 128 ** Invoke sqlite3WalkSelect() for subqueries in the FROM clause and
 129 ** on the compound select chain, p->pPrior.
 130 **
 131 ** If it is not NULL, the xSelectCallback() callback is invoked before
 132 ** the walk of the expressions and FROM clause. The xSelectCallback2()
 133 ** method is invoked following the walk of the expressions and FROM clause,
 134 ** but only if both xSelectCallback and xSelectCallback2 are both non-NULL
 135 ** and if the expressions and FROM clause both return WRC_Continue;
 136 **
 137 ** Return WRC_Continue under normal conditions.  Return WRC_Abort if
 138 ** there is an abort request.
 139 **
 140 ** If the Walker does not have an xSelectCallback() then this routine
 141 ** is a no-op returning WRC_Continue.
 142 */
 143 int sqlite3WalkSelect(Walker *pWalker, Select *p){
 144   int rc;
 145   if( p==0 ) return WRC_Continue;
 146   if( pWalker->xSelectCallback==0 ) return WRC_Continue;
 147   do{
 148     rc = pWalker->xSelectCallback(pWalker, p);
 149     if( rc ) return rc & WRC_Abort;
 150     if( sqlite3WalkSelectExpr(pWalker, p)
 151      || sqlite3WalkSelectFrom(pWalker, p)
 152     ){
 153       return WRC_Abort;
 154     }
 155     if( pWalker->xSelectCallback2 ){
 156       pWalker->xSelectCallback2(pWalker, p);
 157     }
 158     p = p->pPrior;
 159   }while( p!=0 );
 160   return WRC_Continue;
 161 }