Question

我有以下mysql表和一些示例数据。

1）表：ai_shipment

+----+---------------------+---------------------+------------------+
| id | booking_date        | loading_date        | container_number |
+----+---------------------+---------------------+------------------+
|  1 | 2012-08-03 00:00:00 | 2012-08-04 00:00:00 | ABB987987BBC6    |
|  2 | 2012-08-05 00:00:00 | 2012-08-07 00:00:00 | BHJKKU78786GH    |
+----+---------------------+---------------------+------------------+

2）表：ai_purchase_item

+----+---------+----------+-----------+-----------+
| id | item_id | quantity | cost      | rate      |
+----+---------+----------+-----------+-----------+
|  1 |       1 |       50 | 1200.0000 | 1355.0000 |
|  2 |       2 |       20 |  550.0000 |  675.0000 |
|  3 |       4 |       70 |   70.0000 |   70.0000 |
|  4 |       6 |       90 |   90.0000 |   90.0000 |
|  5 |       7 |       80 |   80.0000 |   80.0000 |
+----+---------+----------+-----------+-----------+

3）表：shipment_purchase_item

+----+-------------+------------------+
| id | shipment_id | purchase_item_id |
+----+-------------+------------------+
|  1 |           1 |                2 |
|  2 |           2 |                3 |
+----+-------------+------------------+

基本上我将所有购买的商品详细信息存储在ai_purchase_item，ai_shipment存储运费详情，ai_shipment_purchase_item存储商品的记录。

我想要做的是，我想从ai_purchase_item中选择未发送的所有记录。这意味着ai_shipment_purchase_item中不应存在外键。

参考上述记录，我期望获取的结果是。

+----+---------+----------+-----------+-----------+
| id | item_id | quantity | cost      | rate      |
+----+---------+----------+-----------+-----------+
|  1 |       1 |       50 | 1200.0000 | 1355.0000 |
|  4 |       6 |       90 |   90.0000 |   90.0000 |
|  5 |       7 |       80 |   80.0000 |   80.0000 |
+----+---------+----------+-----------+-----------+

我试过这样的事情（我知道sql查询不合适）

 SELECT 
    pi.id, 
    pi.item_id, 
    pi.quantity, 
    pi.cost,
    pi.rate 
 FROM 
    ai_purchase_item pi 
 JOIN 
    ai_shipment_purchase_item spi ON spi.purchase_item_id = pi.id
 WHERE NOT EXISTS (SELECT spi.purchase_item_id WHERE spi.purchase_item_id = pi.id)

谢谢。

Answer 1

有三种常见的方法可以找到一个表中存在但在MySQL中另一个表中缺少的值：

LEFT JOIN
NOT EXISTS
NOT IN

以下是使用NOT EXISTS的方法：

SELECT 
    pi.id, 
    pi.item_id, 
    pi.quantity, 
    pi.cost,
    pi.rate 
FROM 
    ai_purchase_item AS pi 
WHERE NOT EXISTS
(
    SELECT *
    FROM ai_shipment_purchase_item AS spi
    WHERE spi.purchase_item_id = pi.id
)

这是一个LEFT JOIN：

 SELECT 
    pi.id, 
    pi.item_id, 
    pi.quantity, 
    pi.cost,
    pi.rate 
 FROM 
    ai_purchase_item AS pi 
 LEFT JOIN 
    ai_shipment_purchase_item AS spi ON spi.purchase_item_id = pi.id
 WHERE spi.purchase_item_id IS NULL

这里是NOT IN：

SELECT 
    pi.id, 
    pi.item_id, 
    pi.quantity, 
    pi.cost,
    pi.rate 
FROM 
    ai_purchase_item AS pi 
WHERE pi.id NOT IN
(
     SELECT purchase_item_id
     FROM ai_shipment_purchase_item
)

Quassnoi的以下文章比较了每种方法的表现：

NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL

结论是：

在MySQL中搜索缺失值的最佳方法是使用LEFT JOIN / IS NULL或NOT IN而不是NOT EXISTS。

Answer 2

select * from ai_purchase_item where id not in (select distinct(purchase_item_id) from shipment_purchase_item )

选择所有记录但排除链接记录

2 个答案: