一、IN 、NOT IN
IN 操作符允许在 WHERE 子句中规定多个值。column_name中取值为value1 、value2....的数据会被筛选出来。
(1)in的两种应用场景
select name from student where name in('zhang','wang','zhao');
select * from A where cc in(select cc from B)
(2)in 与 “=”的区别:
select name from student where name in('zhang','wang','zhao');
select name from student where name='zhang' or name='wang' or name='zhao'
*IN 和 NOT IN并不是针对索引的,因此查询会消耗大量时间
二、EXISTX / NOT EXISTS