Question

我在具有两列主键的特定表中遇到GROUP BY查询问题。

我的表看起来像这样：

   CREATE TABLE IF NOT EXISTS `stocks` (
      `id_city` int(10) NOT NULL,
      `id_prod` int(10) NOT NULL,
      `sell_price` int(10) DEFAULT '0',
      PRIMARY KEY (`id_city`,`id_prod`)
    )

假设它插入了这样的值：

INSERT INTO `stocks` (`id_city`, `id_prod`, `sell_price`) 
VALUES ('1', '1', '100'), ('2', '1', '90'), ('3', '1', '10');

经过这样的查询：

SELECT id_prod, id_city, MIN(sell_price)
            FROM stocks 
            GROUP BY id_prod

结果行丢失'id_city'键 - 它首次出现在city_id上，

id_prod     id_city     MIN(sell_price)
1           1           10

如何为此案例构建正确的查询？结果应如下所示：

id_prod     id_city     MIN(sell_price)
1           3           10

Answer 1

如果要返回包含min(sell_price)的记录，可以使用子查询：

SELECT s1.id_prod, 
  s1.id_city, 
  s1.sell_price
FROM stocks s1
inner join
(
  select id_prod,  MIN(sell_price) sell_price
  from stocks
  group by id_prod
) s2
  on s1.id_prod = s2.id_prod
  and s1.sell_price = s2.sell_price

请参阅SQL Fiddle with Demo

返回：

| ID_PROD | ID_CITY | SELL_PRICE |
----------------------------------
|       1 |       3 |         10 |

Answer 2

你的意思是使用max(id_city)

    SELECT id_prod, max(id_city) city , MIN(sell_price)
        FROM stocks 
        GROUP BY id_prod

sql demo

或类似使用count(id_city)

     SELECT id_prod, count(id_city) city, MIN(sell_price)
        FROM stocks 
        GROUP BY id_prod

sql demo

都返回

  ID_PROD   CITY    MIN(SELL_PRICE)
      1        3                10

修改

通过INNER JOIN
尝试此操作
SELECT s.id_prod, s.id_city, s.sell_price FROM stocks s inner join ( select id_prod, MIN(sell_price) sell_price from stocks group by id_prod ) s1 on s.id_prod = s1.id_prod and s.sell_price = s1.sell_price

DEMO SQLFIDDLE

Answer 3

您还必须将id_city添加到GROUP BY子句中

http://www.w3schools.com/sql/sql_groupby.asp

MySQL Group通过查询多个主键表

3 个答案: