php - 关于sql查询php

Question

我想搜索活跃 session 数超过100的终端，我使用的表是terminal_server_log，因为每个终端都有很多日志，我必须确保“时间戳”是最新的。我尝试了两种方式进行搜索。请注意，对于每个终端，最新时间戳并不相同。

$termquery=mysql_query("select distinct(terminal) from
    terminal_server_log where activesession > 100
    group by terminal order by timestamp limit 1");
while($termres=mysql_fetch_array($termquery)){
        $terms=$termres["terminal"];

    array_push($result, array(
          "terminal" => array(
                "type" => "resource",
                "searchvector" => "/tsmon-dev/api/terminal.php?username=$terms",
                "displayvalue" => $terms
                 )
           )
     );
}

echo (json_encode($result)); 

但是，它不起作用。问题是什么？谢谢!

Answer 1

如果你想获取所有 activesession > 100 的终端，那么使用 limit 1 是没有意义的

从terminal_server_log中选择终端，最大(时间戳)，其中activesession > 100按终端分组

它将返回 [terminal, timestamp] 对，其中终端仅具有 activesession>100，并且每条记录的时间戳都是最新的。

如果你想获得一个活跃 session >100且具有最新记录的终端，查询将是:

从terminal_server_log中选择终端，其中activesession > 100 order by timestamp desc limit 1

是的，

please note that the mysql_ constructor is deprecated as of PHP 5.5 //Obsidian Age advised in comments.

已更新

Actually I only want to know the current situation: which terminal's active session is more than 100. I mean, for each terminal, there are a lot of records, if the latest record for this terminal's active session is more than 100, then i choose it

SELECT  a.terminal
FROM    terminal_server_log a
inner join
        (
            SELECT  terminal, MAX(timestamp) timestamp
            FROM    terminal_server_log
            group by terminal
        ) b on (b.terminal=a.terminal and a.timestamp=b.timestamp)
WHERE a.activesession>100