Question

请参阅以下有关我的MySQL表的示例部分：

表格名称： eb_tickets

+-------------------+----------------------+
|  ticket_type      |  time_first_response |
|  Standard Traffic |  0:18:14             |
|  Standard Traffic |  0:48:06             |
|  Miscellaneous    |  44:12:23            |
|  Feed             |  4:48:22             | 
|  Miscellaneous    |  15:33:20            |
|  Banners          |  21:00:02            |
|  Integration      |  36:00:02            |
+-------------------+----------------------+

我想像这样输出响应，用不同的值ASC计算中间值：

+-------------------+----------------------+
|  median_group     |  median              | 
|  Banners          |  21:00:02            |
|  Feed             |  4:48:22             | 
|  Integration      |  36:00:02            |
|  Miscellaneous    |  32:36:13            |
|  Standard Traffic |  0:33:10             |
+-------------------+----------------------+

目前，我通过以下查询来实现这一目标：


    SET @row_number:=0; 
    SET @median_group:='';

    SELECT 
        median_group, AVG(time_first_response) AS median
    FROM
    (SELECT 
        @row_number:=CASE
            WHEN @median_group = ticket_type THEN @row_number + 1
            ELSE 1
        END AS count_of_group,
        @median_group:=ticket_type AS median_group,
        ticket_type,
        time_first_response,
        (SELECT 
                COUNT(*)
            FROM
                eb_tickets
            WHERE
                a.ticket_type = ticket_type) AS total_of_group 
    FROM
        (SELECT 
            ticket_type, time_first_response
        FROM
            eb_tickets           
        ORDER BY ticket_type, time_first_response) AS a) AS b
        WHERE
        count_of_group BETWEEN total_of_group / 2.0 AND total_of_group / 2.0 +1
        GROUP BY median_group

不幸的是，此查询每条记录大约需要1秒钟，而我正在查询数千条记录，ticket_type列可能有20个不同的值。

我正在寻求帮助，以查看是否有可能优化我的当前查询以尝试使查询执行得更快。

谢谢您的帮助！

Answer 1

您可以尝试这样吗？

SELECT counter.ticket_type,AVG(time_first_response) AS median FROM
  (
    SELECT 
      IF(@type = type, @ctr := @ctr + 1, @ctr := 1) AS rownum, 
      @type := ticket_type AS ticket_type,
      time_first_response
    FROM eb_tickets
    ORDER BY ticket_type,time_first_response
  ) AS counter,
  (
    SELECT ticket_type, COUNT(*) AS rows
    FROM eb_tickets
    GROUP BY ticket_type
  ) AS types
  WHERE types.ticket_type = counter.ticket_type AND
    CASE rows % 2 
      WHEN 1 THEN rownum IN (ROUND(rows / 2),ROUND(rows / 2))
      ELSE rownum IN (ROUND(rows / 2),ROUND(rows / 2) + 1)
    END
  GROUP BY counter.ticket_type

编辑：

最初，当我尝试SQL时，我为列使用了较短的名称-type而不是ticket_type，并且子查询counter的列名称为{{1} }，而不是type

优化mysqli查询以使用GROUP BY和ORDER BY计算中位数

1 个答案:

编辑：