Unexpected SUM result found using SUM with JOIN query [closed] - mysql

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I have two tables 'tbl_orders' and 'tbl_instore'. tbl_orders have 'sel_product_qty' which I want to date wise SUM and table(tbl_instore) have 'inst_prod_qty' and 'chln_amount' which I calculate and want to get purchased unit price. But when I use join query on those two tables, the SUM(sel_product_qty) produces double, triple and quadruple amount from the expected result.
Sample data tables are..
Table "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|
+----------+------------+------------+-----------------+---------------+--------------------+
Table "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 |
+----------+----------+------------+---------------+-------------+--------------------+
The following query I have currently tried:
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`;
Which return the following result:
+--------------+---------------+--------+------------+
| 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 |
+--------------+---------------+--------+------------+
If I run the query individually without JOIN, I will get SUM(sel_prod_qty) value as following (also my expected result should be):
+--------------+---------------+--------+------------+
| 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 |
+--------------+---------------+--------+------------+
So, my question is, why does my query return SUM(sel_product_qty) double, triple and quadruple amount from the expected result?

Answer 1

Try this:
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;
I created two sub-query from those tables that you joined because what doesn't work is that you are doing INNER JOIN ... ON tbl_instore.product_id = tbl_orders.product_id. Which if you refer back to your table, those value were repeated multiple times in both tables. Therefore, this sub-queries will perform the mathematical operation and the outer query will only return the results from it.

Answer 2

The pur_uni_price field is not an aggregate field anymore, therefore you need to add it on your GROUP BY. See code below
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))