Question

$sql = "select body, stamp from posts where user_id = '$userid' order by stamp desc";

注意：上面的查询工作正常。我想要做的还是从我的用户表中选择用户名，并显示与user_id匹配的用户名。

我已经编辑了上述声明，但它不起作用。有人可以提出正确的查询吗？我的目标是也能够显示用户名。除了简单地显示user_id。

$sql = "select body, stamp from posts AND username from users where user_id = '$userid' order by stamp desc";

我的目标是也能够显示用户名。而不仅仅是user_id。

Answer 1

您需要使用JOIN将两个表放在匹配字段上，如下所示：

$sql = "SELECT p.body, p.stamp, u.username FROM posts p INNER JOIN users u ON p.user_id=u.user_id WHERE p.user_id='$userid' ORDER BY p.stamp DESC";

Answer 2

您可以使用表名来选择列。例如：

$Query = "select table1.body, table1.stamp, users.username from posts, users where user_id = '$userid' order by stamp desc";

但是，这种方法的表现并不好。

最好的方法是：

$Query = "SELECT table1.body, table1.stamp, users.username 
FROM posts 
INNER/LEFT/RIGHT JOIN users 
ON users.user_id = '$userid' AND users.user_stamp = stamp.stamp_id

所有表格必须相关。

问候，

Answer 3

$sql = "select body, stamp from posts , username from users where user_id = '$userid' order by stamp desc";

我刚刚更正了您的查询中的语法错误...即AND关键字应替换为,。

Answer 4

$sql = "
select body, stamp from posts where user_id = '$userid' order by stamp desc
UNION ALL
select body, stamp from username where user_id = '$userid' order by stamp desc
";

http://dev.mysql.com/doc/refman/5.0/en/union.html

Answer 5

 select body, stamp, username 
    from posts,users 
    where users.user_id = post.user_id 
        and users.user_id = '$userid' 
    order by stamp desc;

Answer 6

您应该使用别名或表名来避免像这样的重复问题

tablename.column

或

alias.column

您可以在where子句中设置别名：

FROM table as alias_name

Answer 7

$sql = "SELECT p.body,p.stamp,u.username from posts p LEFT JOIN users as u ON (p.user_id = u.user_id) WHERE user_id = '$user_id' ORDER BY p.stamp DESC";

应该这样做

Answer 8

试试这个：

select body, stamp, username 
from posts p JOIN users a ON p.user_id = a.user_id 
WHERE p.user_id = '$userid' order by stamp desc

Answer 9

这应该可以正常工作：

SELECT posts.body, posts.stamp, users.username 
FROM posts, users 
WHERE posts.user_id = '$userid' AND posts.user_id = users.user_id
ORDER BY posts.stamp DESC

mysql从两个不同的表中选择。

9 个答案: