MySQL 使用 UNION 连接 3 个表
MySQL joining 3 tables using UNION
这个问题有点长，这样就清楚了，先谢谢了！
简介
我目前有 3 个 table 使用多对多关系。我需要查询所有 3 个 table 并将它们组合成 1 个 table.
问题
我试过这个查询：
SELECT * FROM `login` LEFT JOIN membership ON login.id = membership.login_id UNION SELECT * FROM `login` RIGHT JOIN membership ON login.id = membership.login_id
它 returns:
+----+------+----------+
| id | name | group_id |
+----+------+----------+
| 1 | Tom | 6 |
| 2 | John | 8 |
| 3 | Jane | 4 |
+----+------+----------+
问题
我需要它也包括 group_name。这是我想要的输出：
+----+------+----------+------------+
| id | name | group_id | group_name |
+----+------+----------+------------+
| 1 | Tom | 6 | Red |
| 2 | John | 8 | Brown |
| 3 | Jane | 4 | Purple |
+----+------+----------+------------+
Tables
login Table
A list of all users with auto-increment id
+----+------+
| id | name |
+----+------+
| 1 | Tom |
| 2 | John |
| 3 | Jane |
+----+------+
group Table
A list of all groups with the group_id and group_name
+----------+------------+
| group_id | group_name |
+----------+------------+
| 1 | Green |
| 2 | Blue |
| 3 | Yellow |
| 4 | Purple |
| 5 | Orange |
| 6 | Red |
| 7 | Pink |
| 8 | Brown |
+----------+------------+
membership Table
Stores information on which user belongs to which group
+----------+----------+
| login_id | group_id |
+----------+----------+
| 1 | 6 |
| 2 | 8 |
| 3 | 4 |
+----------+----------+
同时加入 group table 和 select table 中的必填字段。
SELECT l.id,l.name,m.group_id,g.group_name
FROM `login` l
LEFT JOIN `membership` m ON l.id = m.login_id
LEFT JOIN `group` g on g.group_id = m.group_id
试试这个...:)
SELECT
`login`.`id`,
`login`.`name`,
`group`.`group_id`,
`group`.`group_name`
FROM
`membership`
INNER JOIN `login` ON (`membership`.`login_id` = `login`.`id`)
INNER JOIN `group` ON (`membership`.`group_id` = `group`.`group_id`)
这个问题有点长，这样就清楚了，先谢谢了！
简介
我目前有 3 个 table 使用多对多关系。我需要查询所有 3 个 table 并将它们组合成 1 个 table.
问题
我试过这个查询：
SELECT * FROM `login` LEFT JOIN membership ON login.id = membership.login_id UNION SELECT * FROM `login` RIGHT JOIN membership ON login.id = membership.login_id
它 returns:
+----+------+----------+
| id | name | group_id |
+----+------+----------+
| 1 | Tom | 6 |
| 2 | John | 8 |
| 3 | Jane | 4 |
+----+------+----------+
问题
我需要它也包括 group_name。这是我想要的输出：
+----+------+----------+------------+
| id | name | group_id | group_name |
+----+------+----------+------------+
| 1 | Tom | 6 | Red |
| 2 | John | 8 | Brown |
| 3 | Jane | 4 | Purple |
+----+------+----------+------------+
Tables
login Table
A list of all users with auto-increment id
+----+------+
| id | name |
+----+------+
| 1 | Tom |
| 2 | John |
| 3 | Jane |
+----+------+
group Table
A list of all groups with the
group_idandgroup_name
+----------+------------+
| group_id | group_name |
+----------+------------+
| 1 | Green |
| 2 | Blue |
| 3 | Yellow |
| 4 | Purple |
| 5 | Orange |
| 6 | Red |
| 7 | Pink |
| 8 | Brown |
+----------+------------+
membership Table
Stores information on which user belongs to which group
+----------+----------+
| login_id | group_id |
+----------+----------+
| 1 | 6 |
| 2 | 8 |
| 3 | 4 |
+----------+----------+
同时加入 group table 和 select table 中的必填字段。
SELECT l.id,l.name,m.group_id,g.group_name
FROM `login` l
LEFT JOIN `membership` m ON l.id = m.login_id
LEFT JOIN `group` g on g.group_id = m.group_id
试试这个...:)
SELECT
`login`.`id`,
`login`.`name`,
`group`.`group_id`,
`group`.`group_name`
FROM
`membership`
INNER JOIN `login` ON (`membership`.`login_id` = `login`.`id`)
INNER JOIN `group` ON (`membership`.`group_id` = `group`.`group_id`)