mysql INNER_JOIN子查詢

Question

我繼承了一個MySQL數據庫，該數據庫具有如下表：

mysql> describe stock_groups;
+--------+--------------+------+-----+---------+----------------+
| Field  | Type         | Null | Key | Default | Extra          |
+--------+--------------+------+-----+---------+----------------+
| id     | int(11)      | NO   | PRI | NULL    | auto_increment |
| group  | varchar(5)   | YES  |     | NULL    |                |
| name   | varchar(255) | YES  |     | NULL    |                |
| parent | varchar(5)   | YES  |     | NULL    |                |
| order  | int(11)      | YES  |     | NULL    |                |
+--------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

當我運行mysql> select * from stock_groups where group ='D2';

我得到：

mysql> select * from stock_groups where `group`='D2';
+----+-------+------+--------+-------+
| id | group | name | parent | order |
+----+-------+------+--------+-------+
| 79 | D2    | MENS | D      |    51 |
+----+-------+------+--------+-------+
1 row in set (0.00 sec)

而且我有一張桌子：

mysql> describe stock_groups_styles_map;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| group | varchar(5)  | NO   |     | NULL    |                |
| style | varchar(25) | NO   |     | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)

當我跑步時：

mysql> select `group` from stock_groups_styles_map where style='N26';
+-------+
| group |
+-------+
| B1    |
| B11   |
| D2    |
| V2    |
+-------+
4 rows in set (0.00 sec)

我如何獲得stock_groups.name ？

Answer 1

聯接表，然后僅選擇所需的數據。 如果您需要唯一的行，請使用distinct關鍵字：

select  -- If you need unique names, use "select distinct" instead of "select"
    sg.name
from
    stock_groups_styles_map as sgs
    inner join stock_groups as sg on sgs.group = sg.group
where 
    sgs.style = 'N26'

您也可以使用子查詢來解決此問題，但是在這種情況下那將是非常無效的。

重要的事情

您應該在表中添加適當的索引。 它將提高數據庫的性能。

Answer 2

您可以在組列上使用內部聯接

SELECT ss.group, sg.name from 
stock_groups sg inner join stock_groups_styles_map ss on ss.group = sg.group 
where ss.style='N26' 

Answer 3

SELECT stock_groups.name FROM stock_groups_styles_map, stock_groups WHERE stock_groups_styles_map.style ='N26';

為我工作。