Can I Choose Different Table for inner join operation? - tsql

Question

This is my T-SQL
select Id,Profile,Type ,
case Profile
when 'Soft' then 'SID'
when 'Hard' then 'HID'
end as [Profile]
from ProductDetail p1
inner join [tableA or tableB] on xxxxxxxx
I want join tableA when Profile = Soft and join tableB when Profile = Hard, how can I do just only using T-SQL in one batch?
Thanks

Answer 1

You can't directly do it, but could achieve the same effect with outer joins
select Id,Profile,Type ,
case Profile
when 'Soft' then 'SID'
when 'Hard' then 'HID'
end as [Profile]
from ProductDetail p1
left outer join tableA ON tableA.x = p1.x AND p1.Profile = 'Soft'
left outer join tableB ON tableB.x = p1.x AND p1.Profile = 'Hard'
where
where
(tableA.x IS NOT NULL and p1.Profile = 'Soft')
or (tableB.x IS NOT NULL and p1.Profile = 'Hard')

Answer 2

Of course, you can choose different tables for inner join operation, but it must be based on some condition or variable.
For Example:
select Id,Profile,Type ,
case Profile
when 'Soft' then 'SID'
when 'Hard' then 'HID'
end as [Profile]
from ProductDetail p1
inner join tableA A
on Profile='Soft'
AND <any other Condition>
UNION
select Id,Profile,Type ,
case Profile
when 'Soft' then 'SID'
when 'Hard' then 'HID'
end as [Profile]
from ProductDetail p1
inner join tableB B
on Profile='Hard'
AND <any other Condition>

Answer 3

You can do this in a single statement with the same or similar case statement in your join. Below is sample code using temp tables that joins to 2 different reference tables merged into a single result set using a UNION
DECLARE #ProductDetail TABLE (Id INT, sProfile VARCHAR(100), StID INT, HdID INT)
DECLARE #TableA TABLE (StId INT, Field1 VARCHAR(100))
DECLARE #TableB TABLE (HdId INT, Field1 VARCHAR(100))
INSERT INTO #ProductDetail (Id, sProfile, StID , HdID ) VALUES (1,'Soft',1,1)
INSERT INTO #ProductDetail (Id, sProfile, StID , HdID ) VALUES (2,'Hard',2,2)
INSERT INTO #TableA (StId,Field1) VALUES (1,'Soft 1')
INSERT INTO #TableA (StId,Field1) VALUES (2,'Soft 2')
INSERT INTO #TableB (HdId,Field1) VALUES (1,'Hard 1')
INSERT INTO #TableB (HdId,Field1) VALUES (2,'Hard 2')
SELECT
p1.Id,p1.sProfile,
CASE
WHEN p1.sProfile = 'Soft' THEN StID
WHEN p1.sProfile = 'Hard' THEN HdId
END AS [Profile]
,ReferenceTable.FieldName
FROM
#ProductDetail p1
INNER JOIN
(
SELECT StID AS id, 'Soft' AS sProfile, Field1 AS FieldName
FROM #TableA AS tableA
UNION ALL
SELECT HdID AS id, 'Hard' AS sProfile, Field1 AS FieldName
FROM #TableB AS tableB
)
AS ReferenceTable
ON
CASE
WHEN p1.sProfile = 'Soft' THEN StID
WHEN p1.sProfile = 'Hard' THEN HdID
END = ReferenceTable.Id
AND p1.sProfile = ReferenceTable.sProfile
This will return the following result set:
Id sProfile Profile FieldName
1 Soft 1 Soft 1
2 Hard 2 Hard 2