mysql - 在 MYSQL 查询中使用 If

Question

嗨，我目前正在编写一些代码，在从数据库中检索结果之前需要一个 if。

情况是，如果interacterID 不为NULL，则按它过滤，见下文

SELECT *
FROM status
WHERE type != "3"
AND userID = "'.$userID.'"
AND 
(
    interacterID IN ( #IF interacterID is null I want to skip this AND
        SELECT userID
        FROM userFriends
        WHERE (
            userFriends.userID = "'.$currentUserID.'"
            OR userFriends.interacterID = "'.$currentUserID.'"
        )
        AND status = "1"
    )
)
ORDER BY addedDate DESC
LIMIT 1

在此先感谢您的帮助。

Answer 1

如果我没看错，我不确定你是否需要一个 IF （可以这样做）。简单的 IS NULL 和 OR 可用于两种情况：

SELECT *
FROM status
WHERE type != "3"
AND userID = "'.$userID.'"
AND 
(
    interacterID IS NULL OR interacterID IN (
        SELECT userID
        FROM userFriends
        WHERE (
            userFriends.userID = "'.$currentUserID.'"
            OR userFriends.interacterID = "'.$currentUserID.'"
        )
        AND status = "1"
    )
)
ORDER BY addedDate DESC
LIMIT 1    

Answer 2

SELECT *
FROM status
WHERE type != "3"
AND userID = "'.$userID.'"
AND 
(
interacterID IS NOT NULL  (
    SELECT userID
    FROM userFriends
    WHERE (
        userFriends.userID = "'.$currentUserID.'"
        OR userFriends.interacterID = "'.$currentUserID.'"
    )
    AND status = "1"
)
  )
  ORDER BY addedDate DESC
  LIMIT 1  

如果interacterID 为null，则代码不会执行