drop table if exists t1;
CREATE TABLE t1 (field char(1));
INSERT INTO t1 VALUES ('A'),(NULL);
SELECT * from t1 WHERE field IN (NULL);
field
SELECT * from t1 WHERE field NOT IN (NULL);
field
A
SELECT * from t1 where field = field;
field
A
SELECT * from t1 where field <=> field;
field
A
NULL
DELETE FROM t1 WHERE field NOT IN (NULL);
SELECT * FROM t1;
field
NULL
drop table t1;
create table t1 (id int(10) primary key);
insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9);
select * from t1 where id in (2,5,9);
id
2
5
9
drop table t1;