Question

我需要将这两个查询合并为1：

SELECT user1ID AS friendID FROM friends WHERE user2ID = '$userid'
UNION
SELECT user2ID AS friendID FROM friends WHERE user1ID = '$userid'

然后

SELECT firstName, lastName FROM users WHERE ID = friendID (that we just established)

Answer 1

我猜MySQL的UNION（Manual）关键字正是您要找的。

由编辑问题编辑：

您需要一个子查询来处理您想要做的事情（JOIN也可能有用，但会更复杂）：

SELECT firstName, lastName FROM users WHERE ID IN
(
    SELECT user1ID AS friendID FROM friends WHERE user2ID = '$userid'
    UNION
    SELECT user2ID AS friendID FROM friends WHERE user1ID = '$userid'
)

请注意，子查询可能会导致非常大的表和/或复杂查询中出现性能问题。在这种情况下，您可能希望将子查询重构为JOIN。

mySQL SELECT AS用于多个标准

1 个答案: