Question

我有表products和product_prices。这样的

products:
+-------------+----------+
| products_id | title    |
+-------------+----------+
|           1 | phone    |
|           2 | computer |
|           3 | keyboard |
+-------------+----------+


product_prices:
+-------------------+-----------+-------+-------------+
| product_prices_id | productid | price | minquantity |
+-------------------+-----------+-------+-------------+
|                 1 |         1 |   500 |           1 |
|                 2 |         1 |   450 |           2 |
|                 3 |         2 |   800 |           1 |
|                 4 |         2 |   700 |           2 |
|                 5 |         3 |    15 |           1 |
|                 6 |         3 |    10 |           3 |
|                 7 |         3 |     7 |          10 |
+-------------------+-----------+-------+-------------+

因此，数量取决于数量。

我的SQL查询是这样的：

SELECT
   * 
FROM
   products product 
   INNER JOIN
      product_prices price 
      ON price.productid = product.products_id 
GROUP BY
   product.products_id 
ORDER BY
   price.price;

我收到此错误：

Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'price.product_prices_id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

不使用GROUP BY的结果是：

+-------------+----------+-------------------+-----------+-------+-------------+
| products_id | title    | product_prices_id | productid | price | minquantity |
+-------------+----------+-------------------+-----------+-------+-------------+
|           3 | keyboard |                 7 |         3 |     7 |          10 |
|           3 | keyboard |                 6 |         3 |    10 |           3 |
|           3 | keyboard |                 5 |         3 |    15 |           1 |
|           1 | phone    |                 2 |         1 |   450 |           2 |
|           1 | phone    |                 1 |         1 |   500 |           1 |
|           2 | computer |                 4 |         2 |   700 |           2 |
|           2 | computer |                 3 |         2 |   800 |           1 |
+-------------+----------+-------------------+-----------+-------+-------------+

我想做的是，获得价格最低的行，并按products_id分组；

+-------------+----------+-------------------+-----------+-------+-------------+
| products_id | title    | product_prices_id | productid | price | minquantity |
+-------------+----------+-------------------+-----------+-------+-------------+
|           3 | keyboard |                 7 |         3 |     7 |          10 |
|           1 | phone    |                 2 |         1 |   450 |           2 |
|           2 | computer |                 4 |         2 |   700 |           2 |
+-------------+----------+-------------------+-----------+-------+-------------+

我认为我需要使用MIN（），但是我已经尝试了好几种方法，但是都没有用。我能做的最接近的是按价格订购，限制为1，但它只返回1种产品。
有什么想法吗？

如果有帮助，这是我使用的示例数据库的转储：https://transfer.sh/dTvY4/test.sql

Answer 1

您首先需要确定每种产品的最低价格是多少。为此，您可以使用_icdf-aggregate函数。在选择具有聚合功能的常规columnn时，需要在MIN子句中列出常规列。

一旦您知道每种产品的最低价格，您只需从两个表的联接中选择这些行：

GROUP BY

请参见SQLFiddle。

在查询中，您尝试使用没有聚合函数的select p.products_id, p.title, pr.product_prices_id, pr.productid, pr.price, pr.minquantity from product_prices pr join products p on p.products_id=pr.productid join ( select productid, min(price) as minprice from product_prices group by productid ) mpr on mpr.productid=pr.productid and mpr.minprice=pr.price子句，因此出现错误。另外，您缺少MIN逻辑。

与其将文件链接到问题，还不如为其创建一个SQLFiddle / db-fiddle。这样，回答问题就容易得多了。

MySQL获得每个产品组的列值最小的行

1 个答案: