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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
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
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
drop table if exists t1;
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) 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;
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";
UPDATE t1 SET d=1/NULL;
UPDATE t1 SET d=NULL;
INSERT INTO t1 (a) values (null);
Column 'a' cannot be null
INSERT INTO t1 (a) values (1/null);
Column 'a' cannot be null
INSERT INTO t1 (a) values (null),(null);
INSERT INTO t1 (b) values (null);
Column 'b' cannot be null
INSERT INTO t1 (b) values (1/null);
Column 'b' cannot be null
INSERT INTO t1 (b) values (null),(null);
INSERT INTO t1 (c) values (null);
Column 'c' cannot be null
INSERT INTO t1 (c) values (1/null);
Column 'c' cannot be null
INSERT INTO t1 (c) values (null),(null);
INSERT INTO t1 (d) values (null);
Column 'd' cannot be null
INSERT INTO t1 (d) values (1/null);
Column 'd' cannot be null
INSERT INTO t1 (d) values (null),(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(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;
EXPLAIN SELECT * FROM t1 WHERE i=2 OR i IS NULL;
table type possible_keys key key_len ref rows Extra
t1 range i i 5 NULL 10 Using where; Using index
ALTER TABLE t1 CHANGE i i int NOT NULL;
EXPLAIN SELECT * FROM t1 WHERE i=2 OR i IS NULL;
table type possible_keys key key_len ref rows Extra
t1 range i i 4 NULL 7 Using where; Using index
DROP TABLE t1;
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