PHP+MYSQL max min 与limit匹配的问题（急）

[wafer_lee]

我想求出数据库里面新增加的数据的平均值、最大最小值：

select A  as A_vf from (SELECT A FROM Adata ORDER BY fkey desc LIMIT $num)yy

//$num是新增加的数据行数


为什么没有反应呢？？？

[wafer_lee]

求指教！dddd

[wafer_lee]

PHP内的代码如下：

$sqlstr_max_vf = "select Max(vf) as Vmax_vf from (SELECT vf FROM tdata ORDER BY fkey desc )yy LIMIT $num"; 

$res_max_vf = mysql_query($sqlstr_max_vf,$con) or die("ddddd");
           $pid_max_vf = mysql_result($res_max_vf,0,"Vmax_vf"); 

[wafer_lee]

另外，在MYSQL可以执行。但是在程序里面不能执行。而且提交速度非常 慢！

[woqutech]

select A as A_vf from (SELECT A FROM Adata ORDER BY fkey desc LIMIT $num)yy 和 select Max(vf) as Vmax_vf from (SELECT vf FROM tdata ORDER BY fkey desc )yy LIMIT $num 表达的意思不一样吧？limit在内部和外部，你想要查的到底是什么列？

[wafer_lee]

引用 4 楼 woqutech 的回复:

select A as A_vf from (SELECT A FROM Adata ORDER BY fkey desc LIMIT $num)yy 和 select Max(vf) as Vmax_vf from (SELECT vf FROM tdata ORDER BY fkey desc )yy LIMIT $num 表达的意思不一样吧？limit在内部……

把limit $num放（）里面也试了，不行。。。。谢谢了，能再帮忙看看？

[wafer_lee]

引用 4 楼 woqutech 的回复:

select A as A_vf from (SELECT A FROM Adata ORDER BY fkey desc LIMIT $num)yy 和 select Max(vf) as Vmax_vf from (SELECT vf FROM tdata ORDER BY fkey desc )yy LIMIT $num 表达的意思不一样吧？limit在内部……

我的code是这样的：

$sqlstr_max_vf = "select Max(vf) as Vmax_vf from (SELECT vf FROM tdata ORDER BY fkey desc LIMIT $num )yy "; 
 
$res_max_vf = mysql_query($sqlstr_max_vf,$con) or die("ddddd");
           $pid_max_vf = mysql_result($res_max_vf,0,"Vmax_vf"); 

[ACMAIN_CHM]

引用 3 楼 wafer_lee 的回复:

另外，在MYSQL可以执行。但是在程序里面不能执行。而且提交速度非常 慢！

断点调试，看一下你实际的SQL语句是什么。