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mysql >查询语句
* 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
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