1 create table bug40565(value decimal(4,2)) engine=innodb;
2 insert into bug40565 values (1), (null);
3 update bug40565 set value=NULL;
5 info: Rows matched: 2 Changed: 1 Warnings: 0
6 update bug40565 set value=NULL;
8 info: Rows matched: 2 Changed: 0 Warnings: 0