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 default '', b smallint(6) NOT NULL default 0, c datetime NOT NULL default '0000-00-00 00:00:00', d smallint(6) NOT NULL default 0); 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 1048 Column 'd' cannot be null 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 1048 Column 'a' cannot be null Warning 1048 Column 'a' cannot be null 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 1048 Column 'b' cannot be null Warning 1048 Column 'b' cannot be null 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 1048 Column 'c' cannot be null Warning 1048 Column 'c' cannot be null 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 1048 Column 'd' cannot be null Warning 1048 Column 'd' cannot be null 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 create table t1(i int, key(i)); insert into t1 values(1); insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 select i*2 from t1; insert into t1 values(null); explain select * from t1 where i=2 or i is null; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ref_or_null i i 5 const 9 Using where; Using index select count(*) from t1 where i=2 or i is null; count(*) 10 alter table t1 change i i int not null; Warnings: Warning 1265 Data truncated for column 'i' at row 513 explain select * from t1 where i=2 or i is null; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ref i i 4 const 7 Using index select count(*) from t1 where i=2 or i is null; count(*) 9 drop table t1; set names latin2; create table t1 select null as c00, if(1, null, 'string') as c01, if(0, null, 'string') as c02, ifnull(null, 'string') as c03, ifnull('string', null) as c04, case when 0 then null else 'string' end as c05, case when 1 then null else 'string' end as c06, coalesce(null, 'string') as c07, coalesce('string', null) as c08, least('string',null) as c09, least(null, 'string') as c10, greatest('string',null) as c11, greatest(null, 'string') as c12, nullif('string', null) as c13, nullif(null, 'string') as c14, trim('string' from null) as c15, trim(null from 'string') as c16, substring_index('string', null, 1) as c17, substring_index(null, 'string', 1) as c18, elt(1, null, 'string') as c19, elt(1, 'string', null) as c20, concat('string', null) as c21, concat(null, 'string') as c22, concat_ws('sep', 'string', null) as c23, concat_ws('sep', null, 'string') as c24, concat_ws(null, 'string', 'string') as c25, make_set(3, 'string', null) as c26, make_set(3, null, 'string') as c27, export_set(3, null, 'off', 'sep') as c29, export_set(3, 'on', null, 'sep') as c30, export_set(3, 'on', 'off', null) as c31, replace(null, 'from', 'to') as c32, replace('str', null, 'to') as c33, replace('str', 'from', null) as c34, insert('str', 1, 2, null) as c35, insert(null, 1, 2, 'str') as c36, lpad('str', 10, null) as c37, rpad(null, 10, 'str') as c38; show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `c00` binary(0) DEFAULT NULL, `c01` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c02` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c03` varchar(6) CHARACTER SET latin2 NOT NULL DEFAULT '', `c04` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c05` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c06` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c07` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c08` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c09` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c10` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c11` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c12` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c13` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c14` char(0) CHARACTER SET latin2 DEFAULT NULL, `c15` char(0) CHARACTER SET latin2 DEFAULT NULL, `c16` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c17` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c18` char(0) CHARACTER SET latin2 DEFAULT NULL, `c19` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c20` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c21` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c22` varchar(6) CHARACTER SET latin2 DEFAULT NULL, `c23` varchar(9) CHARACTER SET latin2 DEFAULT NULL, `c24` varchar(9) CHARACTER SET latin2 DEFAULT NULL, `c25` varchar(12) CHARACTER SET latin2 DEFAULT NULL, `c26` varchar(7) CHARACTER SET latin2 DEFAULT NULL, `c27` varchar(7) CHARACTER SET latin2 DEFAULT NULL, `c29` varchar(381) CHARACTER SET latin2 DEFAULT NULL, `c30` varchar(317) CHARACTER SET latin2 DEFAULT NULL, `c31` varchar(192) CHARACTER SET latin2 DEFAULT NULL, `c32` char(0) CHARACTER SET latin2 DEFAULT NULL, `c33` varchar(3) CHARACTER SET latin2 DEFAULT NULL, `c34` varchar(3) CHARACTER SET latin2 DEFAULT NULL, `c35` varchar(3) CHARACTER SET latin2 DEFAULT NULL, `c36` varchar(3) CHARACTER SET latin2 DEFAULT NULL, `c37` varchar(10) CHARACTER SET latin2 DEFAULT NULL, `c38` varchar(10) CHARACTER SET latin2 DEFAULT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 drop table t1; select case 'str' when 'STR' then 'str' when null then 'null' end as c01, case 'str' when null then 'null' when 'STR' then 'str' end as c02, field(null, 'str1', 'str2') as c03, field('str1','STR1', null) as c04, field('str1', null, 'STR1') as c05, 'string' in ('STRING', null) as c08, 'string' in (null, 'STRING') as c09; c01 c02 c03 c04 c05 c08 c09 str str 0 1 2 1 1 set names latin1;