php - SQL查询简单题

Question

只是想知道我是否遗漏了什么:

$sql = "SELECT DISTINCT usr.id, 
CONCAT(usr.username, '".PHP_EOL."' ) as username 
FROM #__ads AS a 
RIGHT JOIN #__users 
WHERE gid= '19' AS usr  
    ON usr.id = a.userid 
ORDER BY usr.username";

当我删除 WHERE gid = '19' 部分时它起作用了，它是在错误的地方吗？ gid 列仅存在于 __users 表中。

谢谢!

编辑:知道了，只需要将 Where 子句放在 ORDER BY 之前。

Answer 1

where 子句必须出现在任何连接之后:

$sql = "SELECT DISTINCT usr.id
             , CONCAT(usr.username, '".PHP_EOL."' ) as username
        FROM #__ads AS a
        RIGHT JOIN #__users AS usr
        ON usr.id = a.userid 
        WHERE gid= '19'
        ORDER BY usr.username";