?
* 查询多条不重复记录
? id name
? 1 a
? 2 b
? 3 c
? 4 c
? 5 b
select id, name from s1 group by name
1 a
2 b
3 c
5 b
?
* 查询重复记录最多的记录
SELECT keyword, count( * ) AS count ?
FROM article_keyword ?
GROUP BY keyword ?
ORDER BY count DESC ?
LIMIT 20?
?
* 查询重复记录和重复次数
select user_name,count(*) as count from user_table group by user_name having count>1;
?
?* 多联查询
s1表
id name
3 ? ?a
?
s2表
id s1_id age?
1 ? 2 ? ? 12
2 ? 3 ? ? 23
?
SELECT * FROM `s2` WHERE `s1_id` = (SELECT id FROM `s1` WHERE `name` = 'a');
?
结果?
2 ? 3 ? ? 23
?