MySQL 将字段连接到结果集

Question

我有一个结果集，我需要连接另一个表中的相关字段。

我有以下两个表。 第一个表“组件”保存有关组件的信息:

+----+-------+------------+-----------+
| id | name  | serial_num | model_num |
+----+-------+------------+-----------+
|  1 | comp1 | 0000       | AAAA      |
|  2 | comp2 | 0001       | AAAB      |
|  3 | comp1 | 0010       | AABA      |
|  4 | comp2 | 0011       | AABB      |
|  5 | comp3 | 0100       | ABAA      |
|  6 | comp1 | 0101       | AAAA      |
+----+-------+------------+-----------+

第二个表“componentLog”跟踪组件在不同时间段所属的系统:

+-------------+-----------+---------+---------+-------+
| action_date | component | system  | action  | notes |
+-------------+-----------+---------+---------+-------+
| 2010-01-01  |         1 | CZMIL01 | added   | NULL  |
| 2010-02-25  |         1 | CZMIL01 | removed | NULL  |
| 2010-01-01  |         2 | CZMIL01 | added   | NULL  |
| 2010-02-03  |         2 | CZMIL01 | removed | NULL  |
| 2010-02-03  |         2 | CZMIL02 | added   | NULL  |
| 2010-01-14  |         3 | CZMIL02 | added   | NULL  |
| 2010-01-14  |         4 | CZMIL02 | added   | NULL  |
| 2010-02-03  |         4 | CZMIL02 | removed | NULL  |
| 2010-02-03  |         4 | CZMIL01 | added   | NULL  |
| 2010-01-14  |         5 | CZMIL02 | added   | NULL  |
| 2010-02-25  |         6 | CZMIL01 | added   | NULL  |
+-------------+-----------+---------+---------+-------+

我有一个查询，可以告诉我在指定日期指定系统中有哪些组件:

SELECT *
FROM components
WHERE id IN (
SELECT component
FROM componentLog
WHERE action_date <= '2010-02-25'
AND system = 'CZMIL01'
)
AND id NOT IN (
SELECT component
FROM componentLog
WHERE action_date <= '2010-02-25'
AND system = 'CZMIL01'
AND action = 'removed'
)
ORDER BY name;

此查询提供以下结果集:

+----+-------+------------+-----------+
| id | name  | serial_num | model_num |
+----+-------+------------+-----------+
|  6 | comp1 | 0101       | AAAA      |
|  4 | comp2 | 0011       | AABB      |
+----+-------+------------+-----------+

我需要的是将“componentLog”表中的“action_date”字段连接到此结果集，从而指定组件添加到系统的时间。

Answer 1

只需加入具有所有必需条件的表即可。

SELECT c.*,cl.action_date
FROM components c
JOIN componentLog cl on c.id = cl.component
WHERE action_date <= '2010-02-25'
AND system = 'CZMIL01'
AND action <> 'removed'
ORDER BY name;

如果需要从结果中排除给定系统至少有一个removed操作的组件，请使用

select t.*, cl.action_date
from (
select * from components c
where not exists (select 1 from componentlog 
                  where component = c.id and action = 'removed' 
                  and system = 'CZMIL01' and action_date <= '2010-02-25')
) t
join componentLog cl on cl.component = t.id 
WHERE system = 'CZMIL01' and action_date <= '2010-02-25'
ORDER BY name;