我有两个表 orderedproducts 和 productsinstocks。这是表结构:
订购产品表:
+-----+---------+-----------+----------+--------------+
| id | orderid | productid | quantity | productgroup |
+-----+---------+-----------+----------+--------------+
| 117 | 1016186 | 265385 | 5 | Main |
| 118 | 1016186 | 407454 | 6 | Main |
| 119 | 1016186 | 975045 | 7 | Main |
| 120 | 1016186 | 975046 | 8 | Main |
+-----+---------+-----------+----------+--------------+
productsinstocks 表:
+----+---------+-----------+----------+
| id | stockid | productid | quantity |
+----+---------+-----------+----------+
| 20 | 903958 | 265385 | 200 |
| 21 | 903958 | 407454 | 205 |
| 22 | 903958 | 975045 | 210 |
+----+---------+-----------+----------+
如您所见,库存在 orderedproducts 表中只有三种类型的产品。我想 JOIN 这些表以获得以下结果:
+---------+-----------+---------+-----------+------------+
| orderid | productid | stockid | order_qty | stock_qty |
+---------+-----------+---------+-----------+------------+
| 1016186 | 265385 | 903958 | 5 | 200 |
| 1016186 | 407454 | 903958 | 6 | 205 |
| 1016186 | 975045 | 903958 | 7 | 210 |
| 1016186 | 975046 | 903958 | 8 | NULL |
+---------+-----------+---------+-----------+------------+
我使用了以下查询:
SELECT op.orderid, op.productid, plo.stockid, op.quantity order_qty, plo.quantity stock_qty FROM orderedproducts op
LEFT JOIN productsinstocks plo
ON op.productid=plo.productid
WHERE op.orderid=1016186
AND plo.stockid=903958
但它给了我以下结果:
+---------+-----------+---------+-----------+------------+
| orderid | productid | stockid | order_qty | stock_qty |
+---------+-----------+---------+-----------+------------+
| 1016186 | 265385 | 903958 | 5 | 200 |
| 1016186 | 407454 | 903958 | 6 | 205 |
| 1016186 | 975045 | 903958 | 7 | 210 |
+---------+-----------+---------+-----------+------------+
我不知道我错过了什么。
最佳答案
WHERE
子句中的以下条件是导致结果集中丢失记录的原因:
WHERE plo.stockid = 903958
orderedproducts
表中缺失的记录与 productsinstocks
表中的任何记录都不匹配。因此,此记录的 stockid
值为 NULL
,您当前的 WHERE
条件会将其过滤掉。
相反,将检查 OR plo.stockid IS NULL
添加到 WHERE
子句以保留此记录:
SELECT op.orderid, op.productid, plo.stockid, op.quantity order_qty,
plo.quantity AS stock_qty
FROM orderedproducts op
LEFT JOIN productsinstocks plo
ON op.productid = plo.productid
WHERE op.orderid = 1016186 AND
(plo.stockid = 903958 OR plo.stockid IS NULL)
此处演示:
SQLFiddle
关于MySQL - 使用 LEFT JOIN 会产生意想不到的结果,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40436661/