drop table if exists t1; 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 explain extended 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; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1003 select NULL AS `NULL`,NULL AS `NULL`,isnull(NULL) AS `isnull(null)`,isnull((1 / 0)) AS `isnull(1/0)`,isnull(((1 / 0) = NULL)) AS `isnull(1/0 = null)`,ifnull(NULL,1) AS `ifnull(null,1)`,ifnull(NULL,_latin1'TRUE') AS `ifnull(null,"TRUE")`,ifnull(_latin1'TRUE',_latin1'ERROR') AS `ifnull("TRUE","ERROR")`,isnull((1 / 0)) AS `1/0 is null`,(1 is not null) AS `1 is not null` 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),(1<NULL)+0.0,NULL regexp "a",null like "a%","a%" like null; strcmp("a",NULL) (1<NULL)+0.0 NULL regexp "a" null like "a%" "a%" like null NULL NULL NULL NULL NULL select concat("a",NULL),replace(NULL,"a","b"),replace("string","i",NULL),replace("string",NULL,"i"),insert("abc",1,1,NULL),left(NULL,1); concat("a",NULL) replace(NULL,"a","b") replace("string","i",NULL) replace("string",NULL,"i") insert("abc",1,1,NULL) left(NULL,1) NULL NULL NULL NULL NULL NULL select repeat("a",0),repeat("ab",5+5),repeat("ab",-1),reverse(NULL); repeat("a",0) repeat("ab",5+5) repeat("ab",-1) reverse(NULL) abababababababababab NULL select field(NULL,"a","b","c"); field(NULL,"a","b","c") 0 select 2 between null and 1,2 between 3 AND NULL,NULL between 1 and 2,2 between NULL and 3, 2 between 1 AND null; 2 between null and 1 2 between 3 AND NULL NULL between 1 and 2 2 between NULL and 3 2 between 1 AND null 0 0 NULL NULL NULL explain extended select 2 between null and 1,2 between 3 AND NULL,NULL between 1 and 2,2 between NULL and 3, 2 between 1 AND null; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1003 select (2 between NULL and 1) AS `2 between null and 1`,(2 between 3 and NULL) AS `2 between 3 AND NULL`,(NULL between 1 and 2) AS `NULL between 1 and 2`,(2 between NULL and 3) AS `2 between NULL and 3`,(2 between 1 and NULL) AS `2 between 1 AND null` SELECT NULL AND NULL, 1 AND NULL, NULL AND 1, NULL OR NULL, 0 OR NULL, NULL OR 0; NULL AND NULL 1 AND NULL NULL AND 1 NULL OR NULL 0 OR NULL NULL OR 0 NULL NULL NULL NULL NULL NULL SELECT (NULL OR NULL) IS NULL; (NULL OR NULL) IS NULL 1 select NULL AND 0, 0 and NULL; NULL AND 0 0 and NULL 0 0 select inet_ntoa(null),inet_aton(null),inet_aton("122.256"),inet_aton("122.226."),inet_aton(""); inet_ntoa(null) inet_aton(null) inet_aton("122.256") inet_aton("122.226.") inet_aton("") NULL NULL NULL NULL NULL explain extended select inet_ntoa(null),inet_aton(null),inet_aton("122.256"),inet_aton("122.226."),inet_aton(""); id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE NULL NULL NULL NULL NULL NULL NULL No tables used Warnings: Note 1003 select inet_ntoa(NULL) AS `inet_ntoa(null)`,inet_aton(NULL) AS `inet_aton(null)`,inet_aton(_latin1'122.256') AS `inet_aton("122.256")`,inet_aton(_latin1'122.226.') AS `inet_aton("122.226.")`,inet_aton(_latin1'') AS `inet_aton("")` create table t1 (x int); insert into t1 values (null); select * from t1 where x != 0; x drop table t1; CREATE TABLE t1 ( indexed_field int default NULL, KEY indexed_field (indexed_field) ); INSERT INTO t1 VALUES (NULL),(NULL); SELECT * FROM t1 WHERE indexed_field=NULL; indexed_field SELECT * FROM t1 WHERE indexed_field IS NULL; indexed_field NULL NULL SELECT * FROM t1 WHERE indexed_field<=>NULL; indexed_field NULL NULL DROP TABLE t1; create table t1 (a int, b int) engine=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; b ifnull(t2.b,"this is null") NULL this is 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; b ifnull(t2.b,"this is null") NULL this is null 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; b ifnull(t2.b,"this is null") NULL this is null NULL this is null drop table t1; 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"; Warnings: Warning 1265 Data truncated for column 'd' at row 1 UPDATE t1 SET d=1/NULL; Warnings: Warning 1265 Data truncated for column 'd' at row 1 UPDATE t1 SET d=NULL; Warnings: Warning 1263 Data truncated, NULL supplied to NOT NULL column 'd' at row 1 INSERT INTO t1 (a) values (null); ERROR 23000: Column 'a' cannot be null INSERT INTO t1 (a) values (1/null); ERROR 23000: Column 'a' cannot be null INSERT INTO t1 (a) values (null),(null); Warnings: Warning 1263 Data truncated, NULL supplied to NOT NULL column 'a' at row 1 Warning 1263 Data truncated, NULL supplied to NOT NULL column 'a' at row 2 INSERT INTO t1 (b) values (null); ERROR 23000: Column 'b' cannot be null INSERT INTO t1 (b) values (1/null); ERROR 23000: Column 'b' cannot be null INSERT INTO t1 (b) values (null),(null); Warnings: Warning 1263 Data truncated, NULL supplied to NOT NULL column 'b' at row 1 Warning 1263 Data truncated, NULL supplied to NOT NULL column 'b' at row 2 INSERT INTO t1 (c) values (null); ERROR 23000: Column 'c' cannot be null INSERT INTO t1 (c) values (1/null); ERROR 23000: Column 'c' cannot be null INSERT INTO t1 (c) values (null),(null); Warnings: Warning 1263 Data truncated, NULL supplied to NOT NULL column 'c' at row 1 Warning 1263 Data truncated, NULL supplied to NOT NULL column 'c' at row 2 INSERT INTO t1 (d) values (null); ERROR 23000: Column 'd' cannot be null INSERT INTO t1 (d) values (1/null); ERROR 23000: Column 'd' cannot be null INSERT INTO t1 (d) values (null),(null); Warnings: Warning 1263 Data truncated, NULL supplied to NOT NULL column 'd' at row 1 Warning 1263 Data truncated, NULL supplied to NOT NULL column 'd' at row 2 select * from t1; a b c d 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 0 0000-00-00 00:00:00 0 drop table t1; create table t1 (a int not null, b int not null, index idx(a)); insert into t1 values (1,1), (2,2), (3,3), (4,4), (5,5), (6,6), (7,7), (8,8), (9,9), (10,10), (11,11), (12,12); explain select * from t1 where a between 2 and 3; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 range idx idx 4 NULL 2 Using where explain select * from t1 where a between 2 and 3 or b is null; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 range idx idx 4 NULL 2 Using where drop table t1; select cast(NULL as signed); cast(NULL as signed) NULL