Question

我只是好奇我是否正确地执行此代码 - 它似乎可以在我的测试服务器上工作，但是我知道要让它一直存在直到我知道我正在使用OR语句正确。

    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

没有。你没有。并且不要使用隐式连接语法...

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

第一步应该是添加括号：

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

如果你混合使用and和or，你可能总是想要使用括号。

逗号连接语法也是某种＆＃34;脏＆＃34;，也许您想以下列方式编写查询，以便更清楚地说明哪个部分是连接以及哪个部分是约束：

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，您可以执行以下任一操作：

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

OR

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

Column1或Column2等于value的位置

3 个答案: