php - mysql使用where获取重复行

Question

pid fid
6   19
7   19
8   19
9   19
7   30
6   30

我有一张这样的桌子。我想选择重复的行，当我发送 19、30 个 id 时使用如下IN子句：

Select pid from tablename where fid IN (19,30);

我想要这些结果

pid
7
6

是否有任何 mysql 语句来获得这些结果？

Answer 1

SELECT pid
FROM tableName
WHERE fid IN (19,30)
GROUP BY pid
HAVING COUNT(*) = 2

fid如果没有为每个定义唯一约束pid，那么你需要在DISTINCT里面COUNT

SELECT pid
FROM tableName
WHERE fid IN (19,30)
GROUP BY pid
HAVING COUNT(DISTINCT fid) = 2

• SQLFiddle 演示

Answer 2

利用distinct

Select distinct pid from tablename where fid IN (19,30);

或查找重复项

select pid from tablename group by fid having count(*)>1

Answer 3

首先，您应该对pid进行分组并计数，然后取出出现多次的pid

SELECT pid, count(*) AS cnt
FROM tablename
WHERE fid IN (19,30)
GROUP BY pid
HAVING cnt > 1

Answer 4

SELECT 
    pid 
FROM tablename 
where fid IN (19,30)
group by 
pid