当我使用PHP MySQL查询时，DISTINCT关键字不起作用

Question

When I using the PHP MySQL query DISTINCT keyword is not working here is my PHP query store data into JSON format

<?php
include("connection.php");
$uid=$_REQUEST['userid'];
$activityname="Change status";
$recentstatus=mysqli_query($cn,"SELECT DISTINCT userstatus,activityid,userid FROM useractivity WHERE userid='$uid' AND activityname='$activityname' ORDER BY activityid DESC ");
while($raw=mysqli_fetch_assoc($recentstatus))
{
    $emparray[] = $raw;      
}
$x['data'][]=$emparray;
$x['status']='OK';
echo json_encode($emparray);  
?>

Answer 1

If you only need to remove duplicates then use DISTINCT. GROUP BY should be used to apply aggregate operators to each group

GROUP BY v DISTINCT