MYSQL就像一个联接，但只需要最新的行? [英] MYSQL like a join but only need the newest row?

问题描述

我想在一个查询中执行以下操作:

I want to do the following but in one query:

$query = mysql_query("SELECT name FROM tbl_users WHERE category = '1'");
while($row = mysql_fetch_assoc($query))
{
$query2 = mysql_query("SELECT datecreated 
                       FROM tbl_comments 
                       ORDER BY datecreated DESC LIMIT 1");
$row2 = mysql_fetch_assoc($query2);
echo $row['name'] . " > " . $row2['datecreated'] ."<br />";
}

有一个用户表和一个注释表，我想显示一个用户列表以及他们旁边的最后一条注释的日期吗?

There is a user table and a comments table, I want to display a list of users and the date of the last comment next to them?

在单个查询中有可能吗?

Is this possible in a single query?

推荐答案

您可以使用以下SQL:

You can do so using the following SQL:

SELECT name,
       (
        SELECT datecreated
          FROM tbl_comments
          WHERE tbl_users.user_id = tbl_comments.user_id
          ORDER BY datecreated LIMIT 1
       )
FROM tbl_users
WHERE category = '1';

或使用:

SELECT tbl_users.name, MAX(datecreated) AS latestcomment
  FROM tbl_users LEFT JOIN tbl_comments ON (tbl_users.user_id = tbl_comments.user_id)
  GROUP BY tbl_users.name;

这篇关于MYSQL就像一个联接，但只需要最新的行?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！