尽管花了一个小时的时间，但解决办法仍然是我。我有一个复杂的查询，它返回SUM（）的错误数据。然而，当我将其剥离为最近的形式时，它会输出正确的数据。但为什么并修复，我无法弄明白。
问题
SELECT po.*, SUM( poo.material_qty ) AS total_items_ordered, suppliers.supplier_name
FROM `purchase_orders` po
LEFT JOIN purchase_orders_items poo ON poo.poid = po.poid
LEFT JOIN suppliers ON suppliers.supplier_id = po.supplier_id
LEFT JOIN materials_batch mb ON mb.purchase_order_no = po.poid
WHERE po_status NOT
IN (
'Fulfilled', 'Cancelled'
)
AND batch_status NOT
IN (
'Arrived', 'Cancelled', 'Refused', 'Missing', 'Damaged', 'Completed'
)
GROUP BY po.poid
ORDER BY date_expected ASC
为＆＃39; total_items_ordered＆＃39;提供了非常不正确的数据。
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+---------------------+-----------------------+
| poid | date_raised | date_expected | supplier_id | job_id | job_item_id | ref_no | sub_total | VAT | total | userid | DN | manual | po_status | total_items_ordered | supplier_name |
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+---------------------+-----------------------+
| 15571 | 2014-06-24 13:32:55 | 2014-06-25 00:00:00 | 1 | 0 | 0 | | 14850.10 | 2970.02 | 17820.12 | 1 | | N | Raised | 545 | John Parker & Son Ltd |
| 15572 | 2014-06-24 13:33:26 | 2014-06-25 00:00:00 | 1 | 0 | 0 | | 997.80 | 199.56 | 1197.36 | 1 | | N | Raised | 80 | John Parker & Son Ltd |
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+---------------------+-----------------------+
2 rows in set (0.00 sec)
然而，当我从查询中删除所有复杂性并运行原始SUM（）时，值是正确的：
mysql> SELECT poid, SUM(material_qty) AS total_items_ordered FROM `purchase_orders_items` GROUP BY poid;
+-------+---------------------+
| poid | total_items_ordered |
+-------+---------------------+
| 15571 | 109 |
| 15572 | 20 |
+-------+---------------------+
2 rows in set (0.00 sec)
任何人都可以了解我在哪里出错吗？我已经在下面列出了所有测试表内容，以防您发现我错过的内容。谢谢！
数据示例
mysql> SELECT * FROM purchase_orders;
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+
| poid | date_raised | date_expected | supplier_id | job_id | job_item_id | ref_no | sub_total | VAT | total | userid | DN | manual | po_status |
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+
| 15571 | 2014-06-24 13:32:55 | 2014-06-25 00:00:00 | 1 | 0 | 0 | | 14850.10 | 2970.02 | 17820.12 | 1 | | N | Raised |
| 15572 | 2014-06-24 13:33:26 | 2014-06-25 00:00:00 | 1 | 0 | 0 | | 997.80 | 199.56 | 1197.36 | 1 | | N | Raised |
+-------+---------------------+---------------------+-------------+--------+-------------+--------+-----------+---------+----------+--------+----+--------+-----------+
2 rows in set (0.00 sec)
mysql> SELECT * FROM purchase_orders_items;
+--------+-------+-------------+--------------+----------------+--------------+--------------------------------------------------+
| poi_id | poid | material_id | material_qty | material_price | material_sku | material_name |
+--------+-------+-------------+--------------+----------------+--------------+--------------------------------------------------+
| 1 | 15571 | 2 | 3 | 100.00 | PKS275282 | 406x140 White Universal Beam (S355) |
| 2 | 15571 | 5 | 10 | 17.40 | 118-64-44 | Test Item (S275) |
| 3 | 15571 | 8 | 1 | 9984.50 | 113-64-21 | A really really really big universal beam (S355) |
| 4 | 15571 | 9 | 77 | 10.00 | 12345 | A thing |
| 5 | 15571 | 10 | 18 | 201.20 | 12-34-56 | 102x230 Narrow Beam (S355) |
| 6 | 15572 | 2 | 6 | 100.00 | PKS275282 | 406x140 White Universal Beam (S355) |
| 7 | 15572 | 5 | 9 | 17.40 | 118-64-44 | Test Item (S275) |
| 8 | 15572 | 9 | 4 | 10.00 | 12345 | A thing |
| 9 | 15572 | 10 | 1 | 201.20 | 12-34-56 | 102x230 Narrow Beam (S355) |
+--------+-------+-------------+--------------+----------------+--------------+--------------------------------------------------+
9 rows in set (0.00 sec)
mysql> SELECT * FROM suppliers;
+-------------+-----------------------+--------------------+--------------+---------------------+-------------------+-----------------------+--------------------------+---------------------+----------------------+
| supplier_id | supplier_name | supplier_telephone | supplier_fax | supplier_added_date | supplier_added_by | supplier_last_updated | supplier_last_updated_by | supplier_assessed | supplier_approved_by |
+-------------+-----------------------+--------------------+--------------+---------------------+-------------------+-----------------------+--------------------------+---------------------+----------------------+
| 1 | John Parker & Son Ltd | 01227 783333 | 0800 521932 | 2014-05-04 15:57:43 | 1 | 2014-06-05 16:38:23 | 1 | 2014-05-04 15:57:43 | 2 |
| 2 | Superior Glass Ltd. | 01825 764766 | 01825 767699 | 2014-05-04 17:48:38 | 1 | 2014-06-04 20:14:16 | 1 | 2014-05-04 17:48:38 | 3 |
| 3 | DTS Origins Ltd. | 01283 3283029 | 01928 303494 | 2014-05-04 17:51:57 | 1 | 2014-05-04 17:53:08 | 1 | 2014-05-04 17:51:57 | 2 |
+-------------+-----------------------+--------------------+--------------+---------------------+-------------------+-----------------------+--------------------------+---------------------+----------------------+
3 rows in set (0.00 sec)
mysql> SELECT * FROM materials_batch;
+-------------------+-------+---------------------+-------------------+------------------+-----+---------+------------+-------------+-------------+--------------+
| material_batch_id | poiid | rcvd_date | purchase_order_no | delivery_note_no | qty | rcvd_by | dn_scanned | material_id | supplier_id | batch_status |
+-------------------+-------+---------------------+-------------------+------------------+-----+---------+------------+-------------+-------------+--------------+
| 1 | 1 | 0000-00-00 00:00:00 | 15571 | | 3 | 0 | No | 2 | 1 | Ordered |
| 2 | 2 | 0000-00-00 00:00:00 | 15571 | | 10 | 0 | No | 5 | 1 | Ordered |
| 3 | 3 | 0000-00-00 00:00:00 | 15571 | | 1 | 0 | No | 8 | 1 | Ordered |
| 4 | 4 | 0000-00-00 00:00:00 | 15571 | | 77 | 0 | No | 9 | 1 | Ordered |
| 5 | 5 | 0000-00-00 00:00:00 | 15571 | | 18 | 0 | No | 10 | 1 | Ordered |
| 6 | 6 | 0000-00-00 00:00:00 | 15572 | | 6 | 0 | No | 2 | 1 | Ordered |
| 7 | 7 | 0000-00-00 00:00:00 | 15572 | | 9 | 0 | No | 5 | 1 | Ordered |
| 8 | 8 | 0000-00-00 00:00:00 | 15572 | | 4 | 0 | No | 9 | 1 | Ordered |
| 9 | 9 | 0000-00-00 00:00:00 | 15572 | | 1 | 0 | No | 10 | 1 | Ordered |
+-------------------+-------+---------------------+-------------------+------------------+-----+---------+------------+-------------+-------------+--------------+
答案 0 :(得分：2)
当您从查询中遗漏GROUP BY时，应该清楚显示错误结果的原因。对于每个表JOIN，返回的行数乘以JOIN找到的行数。
由于materials_batch表每个订单包含多个条目，因此对于订单号15571，结果total_items_ordered乘以5，对于订单号15572，将其乘以4。
尝试以下方法：
SELECT
po.*,
(
SELECT SUM(poo.material_qty)
FROM purchase_orders_items poo
WHERE poo.poid = po.poid
) AS total_items_ordered,
suppliers.supplier_name
FROM `purchase_orders` po
LEFT JOIN suppliers ON suppliers.supplier_id = po.supplier_id
LEFT JOIN materials_batch mb ON mb.purchase_order_no = po.poid
WHERE po_status NOT
IN (
'Fulfilled', 'Cancelled'
)
AND batch_status NOT
IN (
'Arrived', 'Cancelled', 'Refused', 'Missing', 'Damaged', 'Completed'
)
GROUP BY po.poid
ORDER BY date_expected ASC