Declare @ManagerIDs Varchar(100) 
Set @ManagerIDs = '3' 
Select * from HumanResources.Employee 
Where ManagerID IN (@ManagerIDs) 

Declare @ManagerIDs Varchar(100) 
Set @ManagerIDs = '3,6' 
Select * from HumanResources.Employee 
Where ManagerID IN (@ManagerIDs) 
Msg 245, Level 16, State 1, Line 4 
Conversion failed when converting the varchar value '3,6' to data type int. 

Declare @ManagerIDs Varchar(100) 
Set @ManagerIDs = '3,6' 
Declare @SQL Varchar(1000) 
Set @SQL = 
'Select * from HumanResources.Employee 
Where ManagerID IN (' + @ManagerIDs + ')' 
EXEC (@SQL) 

Declare @ManagerIDs Varchar(100) 
Set @ManagerIDs = '3,6' 
DECLARE @XmlStr XML 
SET @XmlStr = 
--Start Tag 
'' + 
--Replace all commas with an ending tag and start a new tag 
REPLACE( @ManagerIDs, ',', '') + 
--End Tag 
'' 

Select @XmlStr 

SELECT x.ManagerID.value('.', 'INT') AS A 
FROM @XmlStr.nodes('//ManagerID') x(ManagerID) 

SELECT * 
FROM HumanResources.Employee 
WHERE ManagerID IN( 
SELECT x.ManagerID.value('.', 'INT') AS A 
FROM @XmlStr.nodes('//ManagerID') x(ManagerID) 
)

SELECT * 
FROM HumanResources.Employee AS A 
INNER JOIN 
(SELECT x.ManagerID.value('.', 'INT') AS ManagerID 
FROM @XmlStr.nodes('//ManagerID') x(ManagerID)) B 
ON A.ManagerID = B.ManagerID