如何将结果合并到一行

Question

我有一个查询，我正在尝试使用 SQL Server 将其合并到 1 行中。 它一直迫使我按Frequency 列分组，但我只想按UserId 分组。谁能告诉我我做错了什么。

代码：

SELECT userid, frequency,
(select count(frequency) where frequency = 1) AS Onetime,
(select count(frequency) where frequency = 2) AS Daily,
(select count(frequency) where frequency = 3) AS Weekly,
(select count(frequency) where frequency = 4) AS Fortnightly,
(select count(frequency) where frequency = 5) AS Monthly,
(select count(frequency) where frequency = 6) AS Quarterly,
(select count(frequency) where frequency = 7) AS SemiAnnual,
(select count(frequency) where frequency = 8) AS Annual
FROM AppTasks
where userid = 'userid@gmail.com'
group by UserID, Frequency

数据：

Answer 1

你能试试这个吗？

SELECT userid,
SUM(CASE WHEN frequency = 1 THEN 1 ELSE 0 END) AS Onetime,
SUM(CASE WHEN frequency = 2 THEN 1 ELSE 0 END) AS Daily,
SUM(CASE WHEN frequency = 3 THEN 1 ELSE 0 END) AS Weekly,
SUM(CASE WHEN frequency = 4 THEN 1 ELSE 0 END) AS Fortnightly,
SUM(CASE WHEN frequency = 5 THEN 1 ELSE 0 END) AS Monthly,
SUM(CASE WHEN frequency = 6 THEN 1 ELSE 0 END) AS Quarterly,
SUM(CASE WHEN frequency = 7 THEN 1 ELSE 0 END) AS SemiAnnual,
FROM AppTasks
where userid = 'userid@gmail.com'
group by UserID;

Answer 2

原始查询不起作用，因为 SELECT 语句包含 7 个子查询，每个子查询计数 所有 记录，其频率由外部查询返回，而不仅仅是用户的。

您可以使用PIVOT 计算特定频率数的计数并将其显示为列：

declare @apptasks table (userid nvarchar(20),frequency int)

insert into @apptasks
values
('userid@gmail.com',1),
('userid@gmail.com',2),
('userid@gmail.com',3),
('userid@gmail.com',4),
('userid@gmail.com',5),
('userid@gmail.com',6),
('userid@gmail.com',7),
('userid@gmail.com',7),
('userid@gmail.com',2),
('userid@gmail.com',1),
('userid@gmail.com',1)


select 
    userid, 
    [1] AS Onetime,
    [2] AS Daily,
    [3] AS Weekly,
    [4] AS Fortnightly,
    [5] AS Monthly,
    [6] AS Quarterly,
    [7] AS SemiAnnual
from ( select 
              userid,
              frequency 
       from @apptasks) as source
PIVOT (
    count(frequency) for Frequency in ([1],[2],[3],[4],[5],[6],[7])
) as pvt

结果是

userid            Onetime   Daily   Weekly  Fortnightly Monthly Quarterly   SemiAnnual
userid@gmail.com  3         2       1       1           1       1           2

如果您事先知道要使用哪些值，PIVOT 和 UNPIVOT 就可以工作。 PIVOT 本质上计算 IN 子句中字段（频率）值的聚合（COUNT(*)），并将它们作为以值命名的列返回。

您也可以省略频率值：

select 
    userid, 
    [1] AS Onetime,
    [2] AS Daily,
    [3] AS Weekly,
    [4] AS Fortnightly,
    [5] AS Monthly
from (select userid,frequency from @apptasks) as source
PIVOT 
(
        count(frequency) for Frequency in ([1],[2],[3],[4],[5])
) as pvt

Answer 3

只是因为您只想按 userID 分组，所以从 Select statment as next 中删除 frequency：-

SELECT userid,
(select count(frequency) where frequency = 1) AS Onetime,
(select count(frequency) where frequency = 2) AS Daily,
(select count(frequency) where frequency = 3) AS Weekly,
(select count(frequency) where frequency = 4) AS Fortnightly,
(select count(frequency) where frequency = 5) AS Monthly,
(select count(frequency) where frequency = 6) AS Quarterly,
(select count(frequency) where frequency = 7) AS SemiAnnual,
(select count(frequency) where frequency = 8) AS Annual
FROM AppTasks
where userid = 'userid@gmail.com'
group by UserID