最大数量计算错误

patient_id:1,2,3,4,5,6,7,8,9,10

 $result2=mysql_query("select max(patient_id) as maximum from outdoor");
        $row2= mysql_fetch_array($result2);
      echo $res=$row2['maximum'];

Its taking maximum number as 9 not 10.

try this

$sql = "select max(CONVERT(patient_id,UNSIGNED INTEGER)) as maximum from outdoor";

use this

$sql = "select GREATEST(patient_id) as maximum from outdoor";

Use GREATEST()

Eg:

SELECT GREATEST(2,1);