我有两个表“ tbl_orders”和“ tbl_instore”。 tbl_orders具有“ sel_product_qty”，我想及时确定SUM，表（tbl_instore）具有“ inst_prod_qty”和“ chln_amount”，我计算并希望获得购买的单价。但是，当我在这两个表上使用联接查询时，SUM(sel_product_qty)会从预期结果中产生两倍，三倍和四倍的量。
样本数据表是..
表“ tbl_order”：
+----------+------------+------------+-----------------+---------------+--------------------+
| order_id | ord_det_id | product_id | sel_product_qty | selling_price | order_date_time |
+----------+------------+------------+-----------------+---------------+--------------------+
| 3 | 1 | 4 | 50 | 67.82 | 2019-03-21 21:52:21|
| 4 | 1 | 1 | 100 | 37.88 | 2019-03-21 21:52:21|
| 5 | 2 | 4 | 120 | 67.82 | 2018-03-23 00:02:36|
| 6 | 3 | 3 | 300 | 123.67 | 2019-03-23 00:04:38|
| 7 | 3 | 2 | 50 | 76.28 | 2019-03-23 00:04:38|
| 8 | 4 | 4 | 50 | 67.82 | 2019-03-24 12:13:06|
| 9 | 4 | 2 | 100 | 76.28 | 2019-03-24 12:13:06|
| 10 | 5 | 1 | 10 | 37.88 | 2019-03-25 12:56:40|
| 11 | 5 | 4 | 7 | 67.82 | 2019-03-25 12:56:40|
| 12 | 6 | 4 | 23 | 67.82 | 2019-03-29 00:29:14|
| 13 | 6 | 2 | 25 | 76.28 | 2019-03-29 00:29:14|
| 16 | 7 | 1 | 120 | 37.88 | 2019-04-14 16:51:10|
| 17 | 7 | 3 | 90 | 123.67 | 2019-04-14 16:51:11|
| 18 | 8 | 1 | 100 | 66.95 | 2019-04-22 23:30:39|
| 19 | 8 | 2 | 22 | 70.04 | 2019-04-22 23:30:39|
+----------+------------+------------+-----------------+---------------+--------------------+
表“ tbl_instore”：
+----------+----------+------------+---------------+-------------+--------------------+
| in_st_id | s_inv_id | product_id | inst_prod_qty | chln_amount | instore_date_time |
+----------+----------+------------+---------------+-------------+--------------------+
| 1 | 1 | 1 | 1000 | 65852 | 2/14/2018 17:28 |
| 14 | 9 | 1 | 100 | 6400 | 4/26/2019 8:26 |
| 3 | 2 | 1 | 2000 | 58885 | 3/19/2019 17:32 |
| 5 | 3 | 1 | 100 | 3588 | 3/19/2019 17:35 |
| 11 | 7 | 1 | 1000 | 65000 | 4/22/2019 23:17 |
| 9 | 5 | 1 | 100 | 6345 | 4/20/2019 0:13 |
| 12 | 8 | 2 | 100 | 7800 | 4/22/2019 23:20 |
| 8 | 4 | 2 | 2000 | 144567 | 3/23/2019 0:04 |
| 7 | 4 | 3 | 1000 | 121665 | 3/23/2019 0:04 |
| 13 | 8 | 3 | 150 | 32000 | 4/22/2019 23:20 |
| 15 | 9 | 3 | 100 | 19000 | 4/26/2019 8:26 |
| 10 | 6 | 4 | 1000 | 88022 | 4/20/2019 0:16 |
| 6 | 3 | 4 | 100 | 6582 | 3/19/2019 17:35 |
| 4 | 2 | 4 | 1000 | 65882 | 3/19/2019 17:32 |
| 2 | 1 | 4 | 5000 | 359877 | 2/14/2018 17:28 |
+----------+----------+------------+---------------+-------------+--------------------+
我目前已经尝试过以下查询：
SELECT SUM(tbl_orders.sel_product_qty) AS `sel_prod_qty`,
(SUM(chln_amount) / SUM(inst_prod_qty)) AS `pur_uni_price`,
date_format(`order_date_time`, '%M-%Y') as `month`,
tbl_orders.product_id AS `product_id`
FROM tbl_orders
INNER JOIN tbl_instore ON tbl_instore.product_id = tbl_orders.product_id
WHERE YEAR(`order_date_time`)= '2019'
GROUP BY `month`, `product_id`;
返回以下结果：
+--------------+---------------+--------+------------+
| sel_prod_qty | pur_uni_price | month | product_id |
+--------------+---------------+--------+------------+
| 1320 | 47.923256 | Apr-19 | 1 |
+--------------+---------------+--------+------------+
| 44 | 72.555714 | Apr-19 | 2 |
+--------------+---------------+--------+------------+
| 270 | 138.132 | Apr-19 | 3 |
+--------------+---------------+--------+------------+
| 660 | 47.923256 | Mar-19 | 1 |
+--------------+---------------+--------+------------+
| 350 | 72.555714 | Mar-19 | 2 |
+--------------+---------------+--------+------------+
| 900 | 138.132 | Mar-19 | 3 |
+--------------+---------------+--------+------------+
| 520 | 73.290563 | Mar-19 | 4 |
+--------------+---------------+--------+------------+
如果我在没有JOIN的情况下单独运行查询，我将得到如下的SUM(sel_prod_qty)值（也是我的预期结果）：
+--------------+---------------+--------+------------+
| sel_prod_qty | pur_uni_price | month | product_id |
+--------------+---------------+--------+------------+
| 220 | 47.923256 | Apr-19 | 1 |
+--------------+---------------+--------+------------+
| 22 | 72.555714 | Apr-19 | 2 |
+--------------+---------------+--------+------------+
| 90 | 138.132 | Apr-19 | 3 |
+--------------+---------------+--------+------------+
| 110 | 47.923256 | Mar-19 | 1 |
+--------------+---------------+--------+------------+
| 175 | 72.555714 | Mar-19 | 2 |
+--------------+---------------+--------+------------+
| 300 | 138.132 | Mar-19 | 3 |
+--------------+---------------+--------+------------+
| 130 | 73.290563 | Mar-19 | 4 |
+--------------+---------------+--------+------------+
所以，我的问题是，为什么我的查询从预期结果返回SUM(sel_product_qty)的两倍，三倍和四倍？
答案 0 :(得分：0)
pur_uni_price字段不再是聚合字段，因此您需要将其添加到GROUP BY。参见下面的代码
SELECT SUM(tbl_orders.sel_product_qty) AS `sel_prod_qty`,
(SUM(chln_amount) / SUM(inst_prod_qty)) AS `pur_uni_price`,
date_format(`order_date_time`, '%M-%Y') as `month`,
tbl_orders.product_id AS `product_id`
FROM tbl_orders
INNER JOIN tbl_instore ON tbl_instore.product_id = tbl_orders.product_id
WHERE YEAR(`order_date_time`)= '2019'
GROUP BY `month`, `product_id`, (SUM(chln_amount) / SUM(inst_prod_qty))
答案 1 :(得分：0)
尝试一下：
SELECT `sel_prod_qty`,
`pur_uni_price`,
`month`,
orders.product_id AS `product_id`
FROM
(SELECT product_id,SUM(sel_product_qty) AS `sel_prod_qty`,
DATE_FORMAT(`order_date_time`, '%M-%Y') AS `month`
FROM tbl_orders
WHERE YEAR(`order_date_time`)='2019'
GROUP BY `month`, `product_id`) orders
INNER JOIN
(SELECT product_id,(SUM(chln_amount) / SUM(inst_prod_qty)) AS `pur_uni_price`
FROM tbl_instore GROUP BY product_id) instore
ON orders.product_id=instore.product_id;
我从您加入的那些表中创建了两个子查询，因为行不通是您在做INNER JOIN ... ON tbl_instore.product_id = tbl_orders.product_id。如果您返回表，则会在两个表中多次重复这些值。因此，此子查询将执行数学运算，而外部查询将仅从中返回结果。