如何在 Mysql Select Query 中计算并获取两行的结果？

Question

这是我的表结构。 有时 table1 数据我重复（例如：实际上 Id 1 应该只有 4 行，但有时它是 8 由于重复）所以避免重复我在选择查询中使用 GROUP BY 命令

表 1

|id| website|time|
-----------------
|01|facebook|20.0|
|01|google  |40.0|
|01|youtube |10.0|
|01|ebay    |30.0|
|02|facebook|50.0|
|02|ebay    |50.0|

表 2

    |id|marks|
    ----------- 
    |01|   80|
    |02|   90|
    |03|   70|
    |04|  100|

我想选择特定用户的（标记）、（在 facebook 上的时间） 和 （在 google 和 youtube 上的时间计数）

以下选择查询给出用户 ID '01'的（标记）、（在 facebook 上的时间）

如何在同一查询中接收 id'1' 的 google 和 youtube 的时间计数？

SELECT table2.id,table2.marks, table1.time
FROM table1
RIGHT JOIN table2 ON table1.id= table2.id
WHERE table1.website LIKE ('%facebook%')
AND table1.id=  '01'
GROUP BY table1.id, table1.website

Answer 1

您想在facebook 上找到时间，然后为特定用户找到youtube 和google 的总和，您可以使用mysql conditional sum 来实现它

select
sum(case when t1.website = 'facebook' then t1.time else 0 end) as `fb_time`,
(
  sum(case when t1.website='google' then t1.time else 0 end)+
  sum(case when t1.website='youtube' then t1.time else 0 end)
)
as `google_youtube`,
t2.marks
from table1 t1
join table2 t2 on t1.id = t2.id
where t1.id = '01' 

如果您需要为所有用户计算相同的值，那么您可以这样做

select
t1.id,
sum(case when t1.website = 'facebook' then t1.time else 0 end) as `fb_time`,
(
  sum(case when t1.website='google' then t1.time else 0 end)+
  sum(case when t1.website='youtube' then t1.time else 0 end)
)
as `google_youtube`,
t2.marks
from table1 t1
join table2 t2 on t1.id = t2.id
group by t1.id

Answer 2

如果我正确理解您的查询，我认为您需要使用子查询。 以下子查询返回两个计数； time_on_facebook & time_on_google_and_youtube 所有用户

SELECT t1.id, t2.marks, 
COUNT(t1.time) as time_on_facebook, 
(SELECT COUNT(t1_sq.time)
FROM `table1` as t1_sq
WHERE (t1_sq.website = "youtube" OR t1_sq.website = "google") 
AND t1_sq.id = t1.id
GROUP BY t1.id)  as time_on_google_and_youtube 
FROM `table1` as t1
LEFT JOIN table2 t2 ON t2.id = t1.id
WHERE t1.website = "facebook"
GROUP BY t1.id

要将其限制为用户 id = 01，请添加 WHERE 子句

SELECT t1.id, t2.marks, 
COUNT(t1.time) as time_on_facebook, 
(SELECT COUNT(t1_sq.time)
FROM `table1` as t1_sq
WHERE (t1_sq.website = "youtube" OR t1_sq.website = "google") 
AND t1_sq.id = t1.id
GROUP BY t1.id)  as time_on_google_and_youtube 
FROM `table1` as t1
LEFT JOIN table2 t2 ON t2.id = t1.id
WHERE t1.website = "facebook" AND t1.id = 1
GROUP BY t1.id

您确定要 COUNT(time) 还是要 SUM(time)？ 最后，考虑为两个表添加一个主键，并可能将“id”列重命名为“user_id”以清楚起见。

Answer 3

不清楚您希望输出的样子。我做了一个查询， 但没有尝试。试试看，让我知道它是否有效。

select t1.id, t1.website, sum(t1.time) as total_time, max(t2.marks) as marks 
from table1 as t1
left join table2 as t2
on t1.id = t2.id
where t1.website = 'facebook'
and t1.id = '01'
group by t1.id, t1.website

UNION

select t1.id, t1.website, sum(t1.time) as total_time, max(t2.marks) as marks 
from table1 as t1
left join table2 as t2
on t1.id = t2.id
where t1.website IN ('youtube', 'google')
and t1.id= '01'
group by t1.id, t1.website