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how to write a column expression in a query based on other table value exist


how to write a column expression in a query based on other table value exist

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asita
asita
SSChasing Mays
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Group: General Forum Members
Points: 652 Visits: 337
Hello Please help me here.,

i have below tables called

student (sno, sname, address)
StudentDrillEnrolled (sno, DrillClass)
StudentDrillNotEnrolled (Sno, Reason, Viever)

how to write a query, so that i will have sno,sname,address, Enrolled (Y/N/NA)

enrolled will be calculated
if sno exist in StudentDrillEnrolled table then Y
if sno exist in StudentDrillNotEnrolled table then it is N
if not exist in both tables enrolled & not enrolled then N/A

please help me here

Thanks in advance
asitti
Hotblack
Hotblack
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Group: General Forum Members
Points: 178 Visits: 113
Sounds like you need a couple of left joins and a case - this should do...

SELECT
s.sno
,CASE WHEN e.sno IS NOT NULL THEN
'Y'
WHEN n.sno IS NOT NULL THEN
'N'
WHEN e.sno IS NULL AND n.sno IS NULL THEN
'N/A'
END
FROM student s
LEFT JOIN StudentDrillEnrolled e
ON s.sno=e.sno
LEFT JOIN StudentDrillNotEnrolled n
ON s.sno=n.sno;



ScottPletcher
ScottPletcher
SSCoach
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Group: General Forum Members
Points: 19681 Visits: 7410
Or you can use EXISTS:


SELECT
sno, sname, address,
CASE
WHEN EXISTS(SELECT 1 FROM dbo.StudentDrillEnrolled sde WHERE sde.sno = s.sno) THEN 'Y'
WHEN EXISTS(SELECT 1 FROM dbo.StudentDrillNotEnrolled sdne WHERE sdne.sno = s.sno) THEN 'N'
ELSE 'N/A'
END AS Enrolled
FROM dbo.student s



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