选择最大查询(Ad_number)问题

Question

$r = ca_mysql_query("SELECT MAX(ad_number) FROM `myTable` WHERE  `user` = {$user_id} ");

$max = $r[0]['ad_number'];
echo $max;

它应该打印max ad_number，但它不返回任何值。

如果我尝试从数组中删除最大查询(Ad_number)返回的字段数据。

$r = ca_mysql_query("SELECT * FROM `myTable` WHERE  `user` = {$user_id} ");

$max = $r[0]['ad_number'];

返回给定记录的值。

出什么事了？

Answer 1

为您的列使用别名：

SELECT MAX(ad_number) as max_ad_number FROM myTable WHERE  user = {$user_id}

然后这样做：

$max = $r[0]['max_ad_number']; echo $max;

参见w3schools 这里的文档

Answer 2

$r = ca_mysql_query("SELECT MAX(ad_number) AS AD_NUMBER FROM myTable WHERE user = {$user_id} ");

$max = $r[0]['AD_NUMBER']; 
echo $max;