mysql - SQL COUNT 来自另一个表的行

Question

我正在尝试计算与另一个表中特定行关联的行数

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

但是查询一直返回“moz_admin”表中的总行数

虽然我认为这不是最有效的方法，但这是我所做的

"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];
    }

重点是使它成为一个 SQL 查询，而不是为我循环遍历的每一行查询表。

提前致谢。

Answer 1

您应该将这些组合成一个查询。查询将是:

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;