SQL COUNT來自另一個表的行

Question

我試圖計算與另一個表中的特定行相關聯的行數

SELECT * 
  FROM 
     (
       (SELECT COUNT(*) totalusers 
          FROM mox_admin
             , caspartition 
         WHERE mox_admin.partitionid = caspartition.id
       )
     ) tita
     , caspartition 
 ORDER 
    BY caspartition.id DESC 
 LIMIT 0,5

但查詢會繼續返回“moz_admin”表中的總行數

這是我所做的，雖然我認為不是最有效的方法

"SELECT * FROM caspartition ORDER BY caspartition.id DESC LIMIT 0, 5";
//execute the query then loop through
    while($partition_data = mysqli_fetch_array($result)) {
        $partition_id = $partition_data['id'];
    $subquery_sql = "SELECT COUNT(*) AS totalusers FROM moz_admin WHERE partitionid = '$partition_id'";
        $subquery_sql = mysqli_fetch_array(mysqli_query($conn, $subquery_sql));
        $no_of_users = $subquery_sql[totalusers];
    }

重點是使這個單一的SQL查詢，而不是查詢表中我循環的每一行。

提前致謝。

Answer 1

您應該將這些組合成一個查詢。 查詢將是：

SELECT cp.id, COUNT(a.partitionid) as cnt
FROM (SELECT *
      FROM caspartition
      ORDER BY caspartition.id DESC
      LIMIT 0, 5
     ) cp LEFT JOIN
     moz_admin a
     ON a.partitionid = cp.id
GROUP BY cp.id;