Question

我有3个表，Member_School，其中包含成员与学校之间的链接，Schools，其中包含学校信息，Category，这是用于完整类别名称（成员类别）的简单查找表。

我正在尝试获取每所学校的所有成员类别的计数，但是无法获得特定学校中没有成员的类别的0计数。到目前为止，这是我的查询：

WITH MemberNums AS
(
SELECT School_No, Category, COUNT(Member_No) AS NumberOfMembs

FROM Member_School

WHERE Finish_Date > GETDATE()

AND Category IS NOT NULL

GROUP BY School_No, Category

)


SELECT School.School_No, Category.Category, MemberNums.NumberOfMembs AS NumberOfMembs, School.School_Name, School.ATH_No, School.AWA_No, School.CLE_No, School.CYC_No, School.CYF_No, School.OBS_No, School.PEN_No, School.RHI_No, 
School.STA_No, School.SYL_No

FROM School 

INNER JOIN MemberNums 
ON School.School_No = MemberNums.School_No

LEFT JOIN Category
ON Category.Category_No = MemberNums.Category

ORDER BY School_No

例如，此查询可能为ID为123的学校返回8行，但“类别”表中有10个类别。我想要得到的是每所学校10行，并计算每个类别中的成员人数（包括在Member_School表中没有特定类别记录的学校的零计数）

这是每个表中的示例行：

类别：

Category_No: Cat1
Category: Category1

学校：

School_No: 123
School_Name: Highschool
Memb_No: 10
Secondary: True
Job_No: XJI314
ATH_No: 1
AWA_No: 1
CLE_No: 1
CYC_No: 1
CYF_No: 1
OBS_No: 1
PEN_No: 1
RHI_No: 1
STA_No: 1
SYL_No: 1

会员学校：

Rec_No: 1
Member_No: 2
School_No: 123
Start_Date: 2018-03-19 00:00:00.000
End_Date: 2020-03-19 00:00:00.000
Category: Cat1

Answer 1

如果需要零，请使用cross join生成行，然后引入现有数据：

select s.School_No, c.Category, count(ms.School_No) as NumberOfMembs as NumberOfMembs,
       s.School_Name, s.ATH_No, s.AWA_No, School.CLE_No,
       s.CYC_No, s.CYF_No, s.OBS_No, s.PEN_No, s.RHI_No, 
       s.STA_No, s.SYL_No
from school s cross join
     categories c left join
     Member_School ms
     on ms.School_No = s.School_No and
        ms.Category = c.Category_No and
        ms.Finish_Date > getdate()
group by s.School_No, c.Category, 
         s.School_Name, s.ATH_No, s.AWA_No, School.CLE_No,
         s.CYC_No, s.CYF_No, s.OBS_No, s.PEN_No, s.RHI_No, 
         s.STA_No, s.SYL_No;

Answer 2

使用左联接

WITH MemberNums AS
(
SELECT School_No, Category, COUNT(Member_No) AS NumberOfMembs

FROM Member_School

WHERE Finish_Date > GETDATE()

AND Category IS NOT NULL

GROUP BY School_No, Category

)    

SELECT School.School_No, Category.Category, MemberNums.NumberOfMembs AS NumberOfMembs, School.School_Name, School.ATH_No, School.AWA_No, School.CLE_No, School.CYC_No, School.CYF_No, School.OBS_No, School.PEN_No, School.RHI_No, 
School.STA_No, School.SYL_No

FROM School 

left JOIN MemberNums 
ON School.School_No = MemberNums.School_No

LEFT JOIN Category
ON Category.Category_No = MemberNums.Category

ORDER BY School_No

Answer 3

您是否尝试过使用正确的外部联接？使用正确的外部联接和合并功能以确保显示0而不是null。我在下方发布了一个示例查询

WITH MemberNums AS
(
SELECT School_No, Category, COUNT(Member_No) AS NumberOfMembs

FROM Member_School

WHERE Finish_Date > GETDATE()

AND Category IS NOT NULL

GROUP BY School_No, Category

)


SELECT School.School_No, Category.Category, COALESCE(MemberNums.NumberOfMembs, 0) AS NumberOfMembs, School.School_Name, School.ATH_No, School.AWA_No, School.CLE_No, School.CYC_No, School.CYF_No, School.OBS_No, School.PEN_No, School.RHI_No, 
School.STA_No, School.SYL_No

FROM School 

INNER JOIN MemberNums 
ON School.School_No = MemberNums.School_No

RIGHT OUTER JOIN Category
ON Category.Category_No = MemberNums.Category

ORDER BY School_No

如果您希望来自school和member_school的所有结果都可能没有类别，那么您可能要考虑使用FULL OUTER JOIN

SQL-为分组返回0值

3 个答案: