其中Column1或Column2等於值

Question

我只是好奇我是否在正確執行此代碼-它似乎可以在我的測試服務器上正常工作，但是我很想將其發布，直到我知道我正確使用了OR語句。

    SELECT privatemessages.threadID, privatemessages.messageID, privatemessages.message_body, privatemessages.uid
FROM privatemessages, privatethreads
WHERE privatemessages.threadID =1
AND privatethreads.threadID = privatemessages.threadID
AND privatethreads.to_user
OR privatethreads.from_user =1
LIMIT 0 , 30

Answer 1

不你不是。 而且不要使用隱式連接語法...

SELECT m.threadID
     , m.messageID
     , m.message_body
     , m.uid
  FROM privatemessages m
  JOIN privatethreads t
    ON t.threadID = m.threadID
 WHERE m.threadID = 1
   AND 1 IN (t.to_user,t.from_user)
 LIMIT 0 , 30

Answer 2

第一步應該是添加括號：

SELECT privatemessages.threadID, privatemessages.messageID, privatemessages.message_body, privatemessages.uid
FROM privatemessages, privatethreads
WHERE privatemessages.threadID =1
AND privatethreads.threadID = privatemessages.threadID
AND (privatethreads.to_user
OR privatethreads.from_user =1)
LIMIT 0 , 30

如果您將and和or混合使用，則可能總是想使用括號。

逗號聯接語法也是某種“骯臟的”，也許您想通過以下方式編寫查詢，而不是更清楚地了解聯接的一部分和約束的一部分：

SELECT privatemessages.threadID, privatemessages.messageID, privatemessages.message_body, privatemessages.uid
FROM privatemessages
INNER JOIN privatethreads
  ON privatethreads.threadID = privatemessages.threadID
WHERE privatemessages.threadID =1
AND (privatethreads.to_user
OR privatethreads.from_user =1)
LIMIT 0 , 30

Answer 3

不，您可以執行以下任一操作：

SELECT 
    privatemessages.threadID, 
    privatemessages.messageID, 
    privatemessages.message_body, 
    privatemessages.uid
FROM privatemessages, privatethreads
WHERE privatemessages.threadID =1
AND privatethreads.threadID = privatemessages.threadID
AND (privatethreads.to_user=1 OR privatethreads.from_user =1)
LIMIT 0 , 30

要么

SELECT 
    privatemessages.threadID, 
    privatemessages.messageID, 
    privatemessages.message_body, 
    privatemessages.uid
FROM privatemessages, privatethreads
WHERE privatemessages.threadID =1
AND privatethreads.threadID = privatemessages.threadID
AND 1 IN (privatethreads.to_user, privatethreads.from_user)
LIMIT 0 , 30