Question

Tablename: call
-------------------
|id | name        |
-------------------
| 1 | a           |
| 2 | b           |
| 3 | c           |
| 4 | d           |
| 5 | e           |
-------------------

Tablename: call_detail 
--------------------------------
|id |   detail     | call_id  |
--------------------------------
|1  | note-1       |  1       |
|2  | note-2       |  1       |
|3  | note-3       |  2       |
|4  | note-4       |  2       |
|5  | note-5       |  2       |
|6  | note-6       |  3       |
--------------------------------

需要结果

----------------------
| id | name | detail |
| 1  | a    | note-2 | 
| 2  | b    | note-5 |
| 3  | c    | note-6 |
| 4  | d    | null   |
| 5  | e    | null   |
----------------------

如何离开两个表的最后插入ID

我需要左联接call.id = call_detail.call.id最后一条记录

有没有办法做到这一点

您可以显示一个简单的样本

Answer 1

使用对call_detail表的查询而不是对整个表进行查询的联接，因为在进行联接之前您需要在表中进行过滤才能正确过滤表。您需要使用左联接来完成它。

使用以下查询：

SELECT c.id, c.name, cd.detail
  FROM calls c LEFT JOIN
  (SELECT 
        call_id, 
        MAX(id),
        detail
    FROM call_detail GROUP BY call_id) cd ON cd.call_id = c.id

您可以在这里看到它的工作：SQL Fiddle

注意：由于使用了关键字，我使用名称调用代替了调用。

Answer 2

您需要进行子查询并将其用作虚拟表。像这样：

SELECT call.id, call.name, call_detail.detail
FROM call, 
LEFT JOIN ( select call_id, max(id) as last_call_id from call_detail group by call_id ) call_history ON call.id = call_history.call_id 
LEFT JOIN call_detail ON call_history.last_call_id = call_detail.id

编辑：我添加了左联接：）

Mysql左加入最后一条记录

2 个答案: