select null,\N,isnull(null),isnull(1/0),isnull(1/0 = null),ifnull(null,1),ifnull(null,"TRUE"),ifnull("TRUE","ERROR"),1/0 is null,1 is not null; NULL NULL isnull(null) isnull(1/0) isnull(1/0 = null) ifnull(null,1) ifnull(null,"TRUE") ifnull("TRUE","ERROR") 1/0 is null 1 is not null NULL NULL 1 1 1 1 TRUE TRUE 1 1 select 1 | NULL,1 & NULL,1+NULL,1-NULL; 1 | NULL 1 & NULL 1+NULL 1-NULL NULL NULL NULL NULL select NULL=NULL,NULL<>NULL,IFNULL(NULL,1.1)+0,IFNULL(NULL,1) | 0; NULL=NULL NULL<>NULL IFNULL(NULL,1.1)+0 IFNULL(NULL,1) | 0 NULL NULL 1.1 1 select strcmp("a",NULL),(1NULL; indexed_field NULL NULL DROP TABLE t1;