Convert Exist condition to Join with T-SQL - sql

Question

I am trying to convert the following T-SQL Select query to exclude "Exists" Clause and Include "Join" Clause. but i am ending up not getting the right result. can some one from this expert team help me with some tips.
select *
FROM HRData
INNER JOIN (
SELECT eeceeid, MIN(eecdateoftermination) eTermDate
FROM dbo.empcomp
INNER JOIN
(
SELECT xeeid FROM HRData_EEList
INNER JOIN dbo.empcomp t ON xeeid = eeceeid AND xcoid = eeccoid
WHERE eecemplstatus = 'T' AND eectermreason <> 'TRO' AND eeccoid <> 'WAON6'
AND EXISTS ( SELECT 1 FROM dbo.empded
INNER JOIN dbo.dedcode on deddedcode = eeddedcode AND deddedtype = 'MED' AND (eedbenstopdate IS NULL OR eedbenstopdate > '12/31/2005')
WHERE eedeeid = xeeid AND eedcoid = xcoid )
GROUP BY xeeid
HAVING COUNT(*) > 1) Term ON xeeid = eeceeid
group by eeceeid
) Terms ON eeid = eeceeid AND Termdate = eTermDate

Answer 1

The algorithm to convert EXISTS to JOIN is very simple.
Instead of
FROM A
WHERE EXISTS (SELECT *
FROM B
WHERE A.Foo = B.Foo)
Use
FROM A
INNER JOIN (SELECT DISTINCT Foo
FROM B) AS B
ON A.Foo = B.Foo
But the first one probably will be optimised better

Answer 2

Interesting request.
select *
FROM HRData
INNER JOIN (
SELECT eeceeid, MIN(eecdateoftermination) eTermDate
FROM dbo.empcomp
INNER JOIN
(
SELECT xeeid FROM HRData_EEList
INNER JOIN dbo.empcomp t ON xeeid = eeceeid AND xcoid = eeccoid
INNER JOIN
( SELECT DISTINCT xeeid, xcoid FROM dbo.empded
INNER JOIN dbo.dedcode on deddedcode = eeddedcode AND deddedtype = 'MED' AND (eedbenstopdate IS NULL OR eedbenstopdate > '12/31/2005')
-- WHERE eedeeid = xeeid AND eedcoid = xcoid
) AS A ON xeeid = A.xeeid AND eedcoid = A.eedcoid
WHERE eecemplstatus = 'T' AND eectermreason <> 'TRO' AND eeccoid <> 'WAON6'
GROUP BY xeeid
HAVING COUNT(*) > 1) Term ON xeeid = eeceeid
group by eeceeid
) Terms ON eeid = eeceeid AND Termdate = eTermDate

Answer 3

Another method of converting an exists to a join is to use a ROW_NUMBER() in the subselect to assist in removing duplicates.
EXISTS:
FROM A
WHERE EXISTS (SELECT *
FROM B
WHERE B.Condition = 'true' AND A.Foo = B.Foo)
JOIN:
FROM A
JOIN (SELECT B.Foo, ROW_NUMBER() OVER (PARTITION BY B.Foo ORDER BY B.Foo) RN
FROM B
WHERE B.Condition = 'true') DT
ON A.Foo = DT.Foo AND DT.RN = 1
The ORDER BY is totally arbitrary since you don't care which record it selects, but it's required. You may be able to use (SELECT NULL) instead.