Question

我必须使用表：USERS和DATA。来自user的每个USERS可以在rows上有一个，多个DATA，但也可以有。{/ p>

我还希望users选择USERS而DATA没有对应SELECT USERS.id, USERS.email, USERS.active, USERS.last_alert, DATA.active, DATA.active_from FROM USERS JOIN DATA WHERE DATA.id_user = USERS.id AND DATA.active = 1 ORDER BY USERS.id ASC，但以下查询会省略它们。我应该如何修改它？

DATA.id_user

USERS.id包含{{1}}。

Answer 1

您应该使用LEFT JOIN而不是INNER JOIN

SELECT
    USERS.id,
    USERS.email,
    USERS.active,
    USERS.last_alert,
    DATA.active,
    DATA.active_from
FROM USERS
    LEFT JOIN DATA ON (
        DATA.id_user = USERS.id AND DATA.active = 1
    )
ORDER BY USERS.id ASC

Answer 2

外部加入

SELECT USERS.id,
       USERS.email,
       USERS.active,
       USERS.last_alert,
       DATA.active,
       DATA.active_from
FROM DATA
LEFT OUTER JOIN USERS
WHERE DATA.id_user = USERS.id
    AND DATA.active = 1
ORDER BY USERS.id ASC

Answer 3

将其重写为LEFT JOIN应包含这些行，但不可用的值将变为NULL然后

SELECT USERS.id,
       USERS.email,
       USERS.active,
       USERS.last_alert,
       DATA.active,
       DATA.active_from
FROM USERS
LEFT JOIN DATA ON USERS.id = DATA.id_user AND DATA.active = 1
ORDER BY USERS.id ASC

带有JOIN的SQL SELECT也记录第二个表上没有对应关系

3 个答案: