SQL SELECT名称由id

Question

我需要有关sql查询的帮助.

我有这两个表:

player_locations:

ID |  playerid  | location <- unqiue key
---|-----------------------
 1 |    1       | DOWNTOWN

和 users:

ID  | playername | [..]
----|--------------------
 1  | example1   | ...

我需要一个选择,以获得users.playername从player_locations.playerid.我有独特的地理位置player_locations.playerid.

伪查询:

SELECT playername 
FROM users
WHERE id = player_locations.playerid 
  AND player_locations.location = "DOWNTOWN";

输出应该是example1.

Answer 1

这只是一个简单的问题INNER JOIN.JOIN的一般语法是:

SELECT stuff
FROM table1
JOIN table2 ON table1.relatedColumn = table2.relatedColumn

在您的情况下,您可以使用id来自用户和playerid列的列来关联这两个表player_locations.您还可以'DOWNTOWN'在JOIN声明中包含您的要求.试试这个:

SELECT u.playername
FROM users u
JOIN player_locations pl ON pl.playerid = u.id AND pl.location = 'DOWNTOWN';

编辑

虽然我个人更喜欢上面的语法,但我希望您能够了解另一种编写方法,这与您现在的方法类似.

您还可以使用FROM子句中的逗号从多个表中进行选择以将它们分开.然后,在您的WHERE条款中,您可以插入您的条件:

SELECT u.playername
FROM users u, player_locations pl
WHERE u.id = pl.playerid AND pl.location = 'DOWNTOWN';