Question

TSQL 2008r2。我希望此查询可以返回三行。 SELECT CASE中指定的每个项目一个：

SELECT CASE result 
WHEN 'A' then 'Group A' 
WHEN 'B' then 'Group B' 
WHEN 'C' then 'Group C' 
end as resultType, count(Result) as numberOfResults from masterGroups 
where theYear=2016 and postCode=3579 group by result;

ATM可以正确返回以下内容：

Group A    1
Group C    8

我希望它总是返回三行，而不管它在masterGroups中发现什么。如果未找到三个项目之一，我希望它返回0。因此在上述情况下，它应该返回以下内容：

Group A    1
Group B    8
Group C    0

预先感谢

Answer 1

这里真正想要的是一个包含所有结果类型的表。如果没有这种情况，我们可以为此使用即时CTE：

WITH results AS (
    SELECT 'A' AS result UNION ALL
    SELECT 'B' UNION ALL
    SELECT 'C'
)

SELECT
    CASE r.result 
        WHEN 'A' THEN 'Group A' 
        WHEN 'B' THEN 'Group B' 
        WHEN 'C' THEN 'Group C' 
    END AS resultType,
    COUNT(m.result) AS numberOfResults
FROM results r
LEFT JOIN masterGroups m
    ON r.result = m.result AND m.theYear = 2016 AND m.postCode = 3579
GROUP BY
    r.result;

注意：将当前WHERE子句中的逻辑移至左联接的ON条件。

Answer 2

您也可以通过以下代码实现相同的目的

SELECT CASE groups 
    WHEN 'A' then 'Group A' 
    WHEN 'B' then 'Group B' 
    WHEN 'C' then 'Group C' 
    END AS resultType, 
    COUNT(Result) AS numberOfResults 
FROM (VALUES ('A'), ('B'), ('C')) r (groups)
LEFT JOIN masterGroups m ON m.Result = r.groups
    AND theYear=2016 AND postCode=3579 
GROUP BY groups

OR

FROM (SELECT 'A' UNION SELECT 'B' UNION SELECT 'C') r (groups)
LEFT JOIN masterGroups m ON m.Result = r.groups
    AND theYear=2016 AND postCode=3579 
GROUP BY groups

Answer 3

您可以使用PIVOT和UNPIVOT：

select resultType,numberOfResults
from
(
select 'numresults' numresults,[A]'Group A',[B] 'Group B',[C] 'Group c'
from
( 
select result from masterGroups where theYear=2016 and postCode=3579
)as source
pivot
(
count(result) for result in ([A],[B],[C])
)as p
)ss
unpivot
(
numberOfResults
for resultType in ([Group A], [Group B], [Group c])
)up

如果计数为0或未找到行，则返回每个“选择案例”选项的结果

3 个答案: