我有以下查询,我需要从中提取total_views的中值。
SELECT
@rownum:=@rownum + 1 AS row_num, total_views, projectId
FROM
(SELECT
a.creation,
a.projectId,
devices,
browserIds,
devices + browserIds AS total_views
FROM
((SELECT
projectId, creation
FROM
event
WHERE
kind = 'project_creation'
AND creation > '2017-04-28') a
INNER JOIN ((SELECT
COUNT(DISTINCT deviceId) AS devices, projectId, creation
FROM
event
WHERE
kind = 'open' AND component = 'mobile'
GROUP BY projectId) b
JOIN (SELECT
COUNT(DISTINCT browserId) AS browserIds, projectId, creation
FROM
event
WHERE
kind = 'open' AND component = 'web'
GROUP BY projectId) c ON b.projectId = c.projectId) ON a.projectId = b.projectId
OR a.projectId = c.projectId)
ORDER BY total_views ASC) d,
(SELECT @rownum:=0) e
;
这是结果的一部分:
1 1 151
2 1 256
3 1 301
4 2 404
5 2 305
6 3 895
7 4 654
8 4 369
9 9 874
10 10 123
我需要扩展查询以提取total_views的中值。 有什么想法吗?
答案 0 :(得分:0)
找到解决方案,需要使用@rownum变量的值,而不是使用字段row_num的值来确定中间值的位置。 然后,我计算结果集中间的total_views的平均值。 (如果结果具有偶数行,则平均为两个中间值。如果结果集具有奇数行,则为中间值的平均值,与中间值相同)。 因此使用条件:
WHERE row_num in (CEIL(@rownum/2), FLOOR(@rownum/2))
完整查询:
SELECT avg(total_views) from
(SELECT
@rownum:=@rownum + 1 AS row_num, total_views, projectId
FROM
(SELECT
a.creation,
a.projectId,
devices,
browserIds,
devices + browserIds AS total_views
FROM
((SELECT
projectId, creation
FROM
event
WHERE
kind = 'project_creation'
AND creation > '2017-04-28') a
INNER JOIN ((SELECT
COUNT(DISTINCT deviceId) AS devices, projectId, creation
FROM
event
WHERE
kind = 'open' AND component = 'mobile'
GROUP BY projectId) b
JOIN (SELECT
COUNT(DISTINCT browserId) AS browserIds, projectId, creation
FROM
event
WHERE
kind = 'open' AND component = 'web'
GROUP BY projectId) c ON b.projectId = c.projectId) ON a.projectId = b.projectId
OR a.projectId = c.projectId)
ORDER BY total_views ASC) d,
(SELECT @rownum:=0) e) f WHERE row_num in (CEIL(@rownum/2), FLOOR(@rownum/2))
;