Joining multiple tables results in duplicate rows - sql

Question

There are tow tables (Customer & Feedback) that have different information. The following query is almost correct, except that it results in duplicate rows. I only need unique rows as par customerId and NO for null value.
I tried the GROUP BY clause at the end but it gives error.
Select C.CustomerId,
C.FirstName,
C.LastName,
(SELECT CAST(CASE WHEN F.Id != null or F.Type = 'Query'
THEN 'YES' ELSE 'NO' END AS NVARCHAR(50))) as Query,
(SELECT CAST(CASE WHEN F.Id != null or F.Type = 'Feedback'
THEN 'YES' ELSE 'NO' END AS NVARCHAR(50))) as Feedback
FROM Customer C
LEFT JOIN Feedback F on F.CustomerId= C.CustomerId
Select * from Customer
Select * from Feedback
As Result I want to display only single row by customerId and to join the feedback table data like below...

Answer 1

You May Try either of the Below
SELECT
C.*,
Query = CASE WHEN PVT.Query IS NOT NULL THEN 'Yes' ELSE 'No' END,
Feedback = CASE WHEN PVT.Feedback IS NOT NULL THEN 'Yes' ELSE 'No' END
FROM Customer C
LEFT JOIN FeedBack
PIVOT
(
MAX(Id)
FOR
[Type] IN
(
[Query],[Feedback]
)
)Pvt
ON PVT.CustomerId = c.CustomerId
or Simply
SELECT
C.*,
Query = CASE WHEN EXISTS(SELECT 1 FROM FeedBack WHERE CustomerId = C.CustomerId and [Type]='Query') THEN 'Yes' ELSE 'No' END,
Feedback = CASE WHEN EXISTS(SELECT 1 FROM FeedBack WHERE CustomerId = C.CustomerId and [Type]='Feedback') THEN 'Yes' ELSE 'No' END
FROM Customer C
To Make it more Dynamic ou may Try this
DECLARE #SQL VARCHAR(MAX)
;WITH CTE
AS
(
SELECT
RN = ROW_NUMBER() OVER(PARTITION BY [Type] ORDER BY [Type]),
QRY = LTRIM(RTRIM([Type]))+' = CASE WHEN EXISTS(SELECT 1 FROM FeedBack WHERE CustomerId = C.CustomerId and [Type]='''+LTRIM(RTRIM([Type]))+''') THEN ''Yes'' ELSE ''No'' END'
FROM FeedBack
)
SELECT
#SQL = 'SELECT
C.*'
+SUBSTRING(','+L.List,1,LEN(L.List)-1)
+' FROM Customer C'
FROM
(
SELECT
QRY + ', ' [text()]
FROM CTE
WHERE RN = 1
FOR XML PATH('')
)L(List)
EXEC(#SQL)
Please Refer this Sqlfiddle for detailed example

Answer 2

Select C.CustomerId,
C.FirstName,
C.LastName,
sum(case when F.Type = 'Query' then 1 else 0 end) > 0 as Query,
sum(case when F.Type = 'Feedback' then 1 else 0 end) > 0 as Feedback
FROM Customer C
LEFT JOIN Feedback F on F.CustomerId= C.CustomerId
GROUP BY C.CustomerId, C.FirstName, C.LastName

Answer 3

use case when
Select C.CustomerId,
C.FirstName,
C.LastName,
case when sum(case when F.Type = 'Query' then 1 else 0 end) > 0 then 'Yes' else 'NO' end as Query,
case when sum(case when F.Type = 'Feedback' then 1 else 0 end) > 0 then 'Yes' else 'NO' End as Feedback
FROM Customer C
LEFT JOIN Feedback F on F.CustomerId= C.CustomerId
GROUP BY C.CustomerId, C.FirstName, C.LastName

Answer 4

Try below query using subquery:
select *,case when query=1 then 'Yes' else 'No' end as query,
case when feedback=1 then 'Yes' else 'No' end as feedbackfrom
(select CustomerId, firstname,lastname,
sum(CASE WHEN Type = 'Query'
THEN 1 ELSE 0 END) as Query,
sum(CASE WHEN Type = 'Feedback'
THEN 1 ELSE 0 END) as Feedback from Customer C
LEFT JOIN Feedback F on F.CustomerId= C.CustomerId
group by CustomerId, firstname,lastname)a

Answer 5

Try this:
select c.CustomerId,
c.FirstName,
c.LastName,
case when q.CustomerId is null then 'NO' else 'YES' end Query,
case when f.CustomerId is null then 'NO' else 'YES' end Feedback,
from Customers c
left join (select customerId from Feedback where Type = 'Query' ) q on c.CustomerId = q.CustomerId
left join (select customerId from Feedback where Type = 'Feedback' ) f on c.CustomerId = q.CustomerId