如何在PHP / MySQL中显示选定的列

Question

我在PHP中运行此查询：

$sql="SELECT t.* FROM tickets t join 
(select ticketnumber, max(datetime) as maxdt from ticket_updates tu GROUP BY ticketnumber) tu

ON t.ticketnumber = tu.ticketnumber

WHERE t.status <> 'Completed' AND tu.maxdt < now() - interval 1 hour; ";
$rs=mysql_query($sql,$conn);
while($result=mysql_fetch_array($rs)) {
    echo $result["tu.maxdt"];
}

但它没有显示datetime列

我究竟做错了什么？

Answer 1

您在子选择中选择max(datetime) as maxdt 。 这不会作为tu.maxtd ，需要包含在主选择中

SELECT t.*, max(tu.datetime) as maxdt FROM tickets

echo $result["maxdt"];

暂且不建议使用mysql_函数，您应切换到mysqli_ 。 https://wiki.php.net/rfc/mysql_deprecation

Answer 2

您必须在查询中包括此列：

$sql="SELECT t.*, tu.* FROM tickets t join 
(select ticketnumber, max(datetime) as maxdt from ticket_updates tu GROUP BY ticketnumber) tu

ON t.ticketnumber = tu.ticketnumber

WHERE t.status <> 'Completed' AND tu.maxdt < now() - interval 1 hour; ";

Answer 3

该列称为maxdt而不是tu.maxdt因此需要echo $result['maxdt'] 。 您还需要在select语句中包括该列：

SELECT t.*, tu.* 
FROM tickets t join 
(SELECT ticketnumber, max(datetime) AS maxdt 
 FROM ticket_updates tu 
 GROUP BY ticketnumber) tu 
...