Question

这是我的MySql查询执行的序列：

查询1 ：SET @channel_rank = 0;

查询2：

  SELECT time_of_day, @channel_rank := IF(
        @current_channel = channel,
        1,
        @channel_rank + 1
      ) AS channel_rank , 
      @current_channel := channel AS channel,Views
    FROM
    (
    SELECT @channel_rank = 0,time_of_day,channel, SUM(Views) AS 'Views'
      FROM access_logs_meaningful_optimized
      WHERE `time_of_day` = 0
      AND playing_date = '2016-10-26' GROUP BY channel
      ORDER BY SUM(views) DESC
      LIMIT 5
     ) xx;

示例结果：

time_of_day  channel_rank  channel                Views   
-----------  ------------  ---------------------  --------
          0             1  Tolo                   1291    
          0             2  Tolo News              855     
          0             3  Samaa News             805     
          0             4  Ary Digital            695     
          0             5  Dunya News             653

在这里，我必须首先执行SET @channel_rank = 0;才能将变量（@channel_rank）分配给0.我的问题是 HOW ，在 {{中1}} 我可以将变量（query 2）分配给0，最初使 @channel_rank 独立于 second query 一个。

Answer 1

您不必在子查询中初始化变量。您可以使用CROSS JOIN初始化变量：

SELECT time_of_day, 
       @channel_rank := IF(@current_channel = channel, 1, 
                             @channel_rank + 1) AS channel_rank, 
       @current_channel := channel AS channel,Views
FROM
(
   SELECT time_of_day,channel, SUM(Views) AS 'Views'
   FROM access_logs_meaningful_optimized
   WHERE `time_of_day` = 0
   AND playing_date = '2016-10-26' 
   GROUP BY channel
   ORDER BY SUM(views) DESC
   LIMIT 5
) AS xx
CROSS JOIN (SELECT @channel_rank := 0) var

MySql：在查询

1 个答案: