Question

我有两个表，我正在构建一些统计信息，因此我计算了多个列和表，我的问题是当我尝试加入另一个表并将其分组到嵌套语句中时，我不断得到以下内容我运行代码时出错。

General error: 2014 Cannot execute queries while other unbuffered queries are active...

这是情景：

++============================================================================++
||                               CLIENTS TABLE                                ||
++=======+===============+==============+==============+======================++
|   id   |   firstname   |   lastname   |     email    |      created_at       |
+--------+---------------+--------------+--------------+-----------------------+
|    1   |     JOHN      |      DOE     | john@doe.com |  2014-08-22 20:10:30  |
+--------+---------------+--------------+--------------+-----------------------+
|    2   |     JUNE      |      DAE     | june@dae.com |  2014-07-28 18:12:08  |
+--------+---------------+--------------+--------------+-----------------------+

++============================================================================++
||                               PURCHASES TABLE                              ||
++=======+===============+=============================+======================++
|   id   |   client_id   |     transaction_status      |      created_at       |
+--------+---------------+-----------------------------+-----------------------+
|    1   |        1      |          COMPLETED          |  2014-08-22 20:10:30  |
+--------+---------------+-----------------------------+-----------------------+
|    2   |        2      |          INCOMPLETE         |  2014-08-22 20:10:30  |
+--------+---------------+-----------------------------+-----------------------+
|    1   |        2      |          COMPLETED          |  2014-08-22 20:10:30  |
+--------+---------------+-----------------------------+-----------------------+
|    2   |        1      |          COMPLETED          |  2014-08-22 20:10:30  |
+--------+---------------+-----------------------------+-----------------------+

这是我计算的一些事情：

全球客户总数
客户当月总数
过去一个月的客户总数
最后注册的客户
已完成购买的客户（此操作失败）

最后这是我失败的疑问：

SELECT 
  ( SELECT 
      COUNT(*) 
    FROM
      clients
  ) AS 
      total_registered_clients,

  ( SELECT 
      COUNT(*) 
    FROM 
      clients 
    AND 
      (YEAR(created_at) = YEAR(CURRENT_DATE)) 
    AND 
      (MONTH(created_at) = MONTH(CURRENT_DATE)) 
  ) AS 
      current_month_registered_clients,

  ( SELECT 
      COUNT(*) 
    FROM 
      clients 
    AND 
      created_at 
    BETWEEN 
      (CURRENT_DATE - INTERVAL 1 MONTH) 
    AND 
      CURRENT_DATE 
  ) AS 
      last_month_registered_clients,

  -- This part fails
  ( SELECT
      COUNT(*)
    FROM
      clients
    INNER JOIN
      purchases
    WHERE
      purchases.client_id = clients.id
    AND
      purchases.transaction_status = 'completed'
    GROUP BY
      purchases.client_id
   ) AS
       clients_with_purchases

编辑：我对var_dump的预期结果是：

[0] =>
object(stdClass)#60 (10) {
  ["total_registered_clients"]=>
    string(1) "2"
  ["current_month_registered_clients"]=>
    string(1) "1"
  ["last_month_registered_clients"]=>
    string(1) "1"
  ["clients_with_purchases"]=>
    string(1) "2"

}

Answer 1

删除该错误：

INNER JOIN
      purchases
    ON    -- not WHERE
      purchases.client_id = clients.id

并删除GROUP BY

但是，第三个查询是否试图计算已购买的客户数量或购买数量？（你在计算购买量）

计算已购买客户数量的2种方法

SELECT
      COUNT(DISTINCT clients.id)
FROM clients
      INNER JOIN purchases
                  ON purchases.client_id = clients.id
                        AND purchases.transaction_status = 'completed'

SELECT
      COUNT(*)
FROM clients
WHERE EXISTS (
            SELECT
                  1
            FROM purchases
            WHERE transaction_status = 'completed'
                  AND clients.id = purchases.client_id
      )

Answer 2

SELECT 
  ( SELECT 
      COUNT(*) 
    FROM
      clients
  ) AS 
      total_registered_clients,

  ( SELECT 
      COUNT(*) 
    FROM 
      clients 
    where
      (YEAR(created_at) = YEAR(GETDATE())) 
    AND 
      (MONTH(created_at) = MONTH(GETDATE())) 
  ) AS 
      current_month_registered_clients,

  ( SELECT 
      COUNT(*) 
    FROM 
      clients 
    where 
      created_at 
    BETWEEN 
      (dateadd(m,-1,GETDATE())  ) 
    AND 
      GETDATE() 
  ) AS 
      last_month_registered_clients,

  -- This part fails
  ( SELECT
      COUNT(*)
    FROM
      clients
    INNER JOIN
      purchases
    on
      purchases.client_id = clients.id
    where
      purchases.transaction_status = 'completed'

   ) AS
       clients_with_purchases

MySQL - 使用嵌套分组的嵌套选择

2 个答案: