# Initialise --disable_warnings drop table if exists t1; --enable_warnings # # Testing of NULL in a lot of different places # 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; select 1 | NULL,1 & NULL,1+NULL,1-NULL; select NULL=NULL,NULL<>NULL,IFNULL(NULL,1.1)+0,IFNULL(NULL,1) | 0; select strcmp("a",NULL),(1NULL; DROP TABLE t1; # # Testing of IFNULL # create table t1 (a int, b int) type=myisam; insert into t1 values(20,null); select t2.b, ifnull(t2.b,"this is null") from t1 as t2 left join t1 as t3 on t2.b=t3.a; select t2.b, ifnull(t2.b,"this is null") from t1 as t2 left join t1 as t3 on t2.b=t3.a order by 1; insert into t1 values(10,null); select t2.b, ifnull(t2.b,"this is null") from t1 as t2 left join t1 as t3 on t2.b=t3.a order by 1; drop table t1; # # Test inserting and updating with NULL # CREATE TABLE t1 (a varchar(16) NOT NULL, b smallint(6) NOT NULL, c datetime NOT NULL, d smallint(6) NOT NULL); INSERT INTO t1 SET a = "", d= "2003-01-14 03:54:55"; UPDATE t1 SET d=1/NULL; UPDATE t1 SET d=NULL; --error 1048 INSERT INTO t1 (a) values (null); --error 1048 INSERT INTO t1 (a) values (1/null); INSERT INTO t1 (a) values (null),(null); --error 1048 INSERT INTO t1 (b) values (null); --error 1048 INSERT INTO t1 (b) values (1/null); INSERT INTO t1 (b) values (null),(null); --error 1048 INSERT INTO t1 (c) values (null); --error 1048 INSERT INTO t1 (c) values (1/null); INSERT INTO t1 (c) values (null),(null); --error 1048 INSERT INTO t1 (d) values (null); --error 1048 INSERT INTO t1 (d) values (1/null); INSERT INTO t1 (d) values (null),(null); select * from t1; drop table t1;