Mysql：与多个'where'加入3个表？

Question

我试图在一个条件下将另一个表连接到另一个条件，然后将该表连接到另一个条件上的另一个表。你能做到这一点吗？如果是的话，那么正确的语法是什么？我一直在尝试这个，但它不起作用：

$check = $members->prepare("select users.fname, users.lname, groups.groupid, attributes.max 
    from users 
    JOIN groups 
     on users.user_id = groups.userid 
    where groups.userid = ? 
    LEFT JOIN attributes 
     on users.user_id = attributes.userid 
    where attributes.groupid = ?"); 
$check->bind_param('ss', $_SESSION['token'][1], $which_group); 
$check->execute(); 

欢呼声。

Answer 1

只需使用........ AND

$check = $members->prepare("select users.fname, users.lname, groups.groupid, attributes.max 
    FROM users 
    JOIN groups 
     ON users.user_id = groups.userid 
     AND groups.userid = ? 
    LEFT JOIN attributes 
     ON users.user_id = attributes.userid 
     AND attributes.groupid = ? 

Answer 2

attributes.groupid的测试必须是LEFT JOIN上连接条件的一部分。试图在WHERE子句中测试这个条件会强制LEFT JOIN的行为就像它是一个INNER JOIN一样。

select users.fname, users.lname, groups.groupid, attributes.max 
    from users 
     JOIN groups 
      on users.user_id = groups.userid 
     LEFT JOIN attributes 
      on users.user_id = attributes.userid 
       and attributes.groupid = ? 
    where groups.userid = ? 

Answer 3

如果你指的条件是相关的连接表任何文字，而不是，在将它们组合一个where子句。

select users.fname, users.lname, groups.groupid, attributes.max 
from users 
    JOIN groups 
     on users.user_id = groups.userid 
    LEFT JOIN attributes 
     on users.user_id = attributes.userid 
where groups.userid = ? and attributes.groupid = ?