MySQL JOIN 语法优先级

Question

我有两张 table

members
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| mindex     | smallint(4) | NO   | PRI | NULL    | auto_increment | 
| memberid   | smallint(5) | YES  | MUL | NULL    |                | 
| forenames  | varchar(40) | YES  |     | NULL    |                | 
| surname    | varchar(20) | YES  |     | NULL    |                | 
| nameprefix | varchar(30) | YES  |     | NULL    |                | 
| namesuffix | varchar(50) | YES  |     | NULL    |                | 
| died       | smallint(5) | YES  |     | NULL    |                | 
| notes      | text        | YES  |     | NULL    |                | 
+------------+-------------+------+-----+---------+----------------+

和

memberships;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| mshipindex | smallint(4) | NO   | PRI | NULL    | auto_increment | 
| memberid   | smallint(5) | YES  | MUL | NULL    |                | 
| msid       | smallint(5) | YES  |     | NULL    |                | 
| mstype     | varchar(20) | YES  |     | NULL    |                | 
| msyear     | smallint(5) | YES  |     | NULL    |                | 
| msposition | varchar(15) | YES  |     | NULL    |                | 
+------------+-------------+------+-----+---------+----------------+

我想搜索一年的成员(member)资格(在 memberships.msyear 中)并获取 memberships.mstype 和 members.surname。 我只是无法获得正确的 JOIN 语法。

Answer 1

你将使用这样的东西:

select m.surname,
  s.mstype
from members m
left join memberships s
  on m.memberid = s.memberid
where s.msyear = yourYear

参见SQL Fiddle with Demo

我使用了LEFT JOIN来返回所有成员，甚至是那些可能没有成员记录的成员。如果成员(member)在成员(member)表中没有记录，则返回null。

如果您需要学习 JOIN 语法的帮助，这里有一个很棒的 visual explanation of joins