在mysql中执行groupby时仅选择一行

我没有下表：

mid pid   price
1   100   10
1   200   10
1   300   10
1   400   10
2   500   20
2   600   30
2   700   20
3   800   40
3   900   50

我想找到每个mid的最低价格pid

为此，我查询了这个代码

SELECT t1.mid,t1.pid 
FROM tableName t1
JOIN (
  SELECT mid, min(price) as min_price
  FROM tableName
  GROUP BY mid
) as t2 on t1.mid = t2.mid and t1.price = t2.min_price;

理想情况下，它应该给出结果，但在我的例子中，每组都有多个pid具有相同的价格。因此，它正在打印所有结果

但我只想限制每一个中间的一行

有没有办法做到这一点？ 我有一个 它的工作原理是：

SELECT t1.mid,t1.pid FROM tableName t1 
INNER JOIN ( 
     SELECT mid AS mid1, pid AS pid1, min(price) as min_price FROM  tableName GROUP BY mid 
) as t2
on t1.mid = t2.mid1 and t1.price = t2.min_price and t1.pid = t2.pid1;

试试这个：

试试这个：

select t1.*
from tablename t1
inner join (select mid, min(pid) min_pid from
(select t1.mid,t1.pid
FROM tablename t1
inner join (select mid,
    min(price) as min_price
    FROM tablename
    GROUP BY mid) t2 on t1.mid = t2.mid
and t1.price = t2.min_price) t
group by mid) t2 on t1.mid = t2.mid
and t1.pid = t2.min_pid
;

---

它生成具有最小价格和最小pid的行。

您的数据库中肯定应该有一个自动主键table@e4c5对不起先生,我没听清楚,您能详细说明一下吗?因为pid,mid组合可以复制,所以您需要有一个单独的主键来实现这一点work@YahyaHHussein先生，限制不是解决办法@e4c5先生，如果我能正确理解您的意思，我应该在创建表本身时添加一个主键，如果是的话，应该添加哪个列。请参阅我在评论中多次提到的SQLFIDDLE演示，它在mysql 5.6及更高版本中工作。这是无效的SQL@Jiang检查您对此的查询，而不是working@SRingne我已修改，您可以测试未定义的表名？？运行查询时，表“db_2_36b118.t”不存在。请用表名替换我的表名t。您更改了架构。我想你已经解决了你的问题。真为你高兴。

select s.mid,s.pid,s.price
from
(
SELECT t1.mid,t1.pid,t1.price,
        if (t1.mid <> @p, @rn:=1,@rn:=@rn+1) rn,
        @p:=t1.mid p
FROM (select @rn:=0,@p:=0) rn,t t1 
order by t1.mid,t1.price,t1.pid
) s where s.rn = 1

select t1.*
from tablename t1
inner join (select mid, min(pid) min_pid from
(select t1.mid,t1.pid
FROM tablename t1
inner join (select mid,
    min(price) as min_price
    FROM tablename
    GROUP BY mid) t2 on t1.mid = t2.mid
and t1.price = t2.min_price) t
group by mid) t2 on t1.mid = t2.mid
and t1.pid = t2.min_pid
;