如何选择字段并在SQL中为每个字段计数？

Question

我有一个名为message的SQL表，我想从表中选择DISTINCT用户名，该表将向ID为（$ uid）的收件人发送任何消息，并使用单行查询为每个发件人选择COUNT(message) 。

我已经试过这段代码：

$query="SELECT DISTINCT clientname,user_id,user1pic, COUNT("SELECT id FROM messages WHERE clientname=clientname) AS counted FROM messages WHERE receiver=$uid and status='unread' ";
$messages=mysqli_query($cnx,$query);
while($row=mysqli_fetch_array($cnx,$messages)){

echo '<a class="example" > '.$row['clieenter code herentname'].''.$row['counted'].'</a>' ;}
if(mysqli_num_rows($cnx,$messages)<=0){
    echo '<a class="example" href="#">You Have No Messages</a>' ;
}

Answer 1

请尝试以下操作：

SELECT 
  clientname,
  user_id,
  user1pic, 
  COUNT(1) AS counted 
FROM 
  messages 
WHERE 
  receiver=:uid 
  and status='unread'
Group by
  clientname,
  user_id,
  user1pic;

我已经用参数占位符替换了内联PHP变量-请使用参数绑定来避免SQL注入。