Setting subquery to variable to be used within the IN operator - sql

Question

I would like to use a variable to represent a result set that will be used in the WHERE clause of a query.
SELECT *
FROM Table1
WHERE
Exam1_ID IN (SELECT Id FROM Exam)
OR Exam2_ID IN (SELECT Id FROM Exam)
OR Exam3_ID IN (SELECT Id FROM Exam)
OR Exam4_ID IN (SELECT Id FROM Exam)
I would like to use a variable in place of SELECT Id FROM Exam so I don't have to keep repeating the query. I tried declaring a variable but since the results of the subquery could contain multiple integers I am not sure what the declare the variable as. I went ahead and tried ...
DECLARE #SubQuery INT;
SET #SubQuery = (SELECT Id FROM Exam);
SELECT *
FROM Table1
WHERE
Exam1_ID IN (#SubQuery)
OR Exam2_ID IN (#SubQuery)
OR Exam3_ID IN (#SubQuery)
OR Exam4_ID IN (#SubQuery)
I received the following error ..
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

Answer 1

You'd probably find that this performs better using a WHERE EXISTS like this
SELECT *
FROM Table1 t1
WHERE EXISTS ( SELECT *
FROM Exam e
WHERE t1.Exam1_ID = e.Id
OR t1.Exam2_ID = e.Id
OR t1.Exam3_ID = e.Id
OR t1.Exam4_ID = e.Id)

Answer 2

You can write an exists like this.
SELECT *
FROM Table1 t1
WHERE EXISTS (
SELECT 1 FROM Exam e
WHERE e.Id in ( t1.Exam1_ID , t1.Exam2_ID , t1.Exam3_ID, t1.Exam4_ID )
)

Answer 3

Lets begin from error message
Subquery returned more than 1 value. This is not permitted when the
subquery follows =, !=, <, <= , >, >= or when the subquery is used as
an expression.
The reason is pretty simple, you declared your subquery as INT
So if you will change it to TABLE(Id INT) you will receive new error message.
You can use different ways to solve your problem.
1) Inner join (It can give you duplicates, so I dont know is it valid for you to use this method)
DECLARE #SubQuery TABLE (RecordId INT)
INSERT INTO
#SubQuery
SELECT
Id
FROM
Exam
SELECT *
FROM
Table1 t1
INNER JOIN #Subquery sq
ON sq.Id = t1.Exam1_ID
OR sq.Id = t1.Exam2_ID
OR sq.Id = t1.Exam3_ID
OR sq.Id = t1.Exam4_ID
2) Exist
Please find sample in Rich Benner answer. He posted it while I was typing. But I found one typo there, he used different aliases in exists block
OR t1.Exam2_ID = e.Id --t1 - correct alias
OR t2.Exam2_ID = e.Id --t2 - incorrect
OR t3.Exam2_ID = e.Id --t3 - incorrect
OR t4.Exam2_ID = e.Id --t4 - incorrect