Check constraint in SQL Server - sql

Question

I have three tables a,b and c and need to add a constraint like below for checking the data integrity
The below is wrong but I need help in enforcing the below condition.
ALTER TABLE [a]
ADD CONSTRAINT UOMGROUPIG CHECK UNITOFMEASURID IN (SELECT UnitOfMeasureId FROM b WHERE UOMGroupId=1 )
ALTER TABLE [c]
ADD CONSTRAINT UOMGROUPIG CHECK UNITOFMEASURID IN (SELECT UnitOfMeasureId FROM b WHERE UOMGroupId=2 )
Thanks

Answer 1

A scalar valued function like this works for your example, you can easily modify it and create your second constraint:
CREATE FUNCTION your_schema_name.udf_Check1(
#UNITOFMEASURID INT
)
RETURNS BIT
AS
BEGIN
DECLARE #returnValue BIT = 0
SELECT #returnValue = CASE WHEN COUNT(UnitOfMeasureId) > 0 THEN 1 ELSE 0 END
FROM your_schema_name.b
WHERE UOMGroupId=1
AND #UNITOFMEASURID = UnitOfMeasureId
RETURN #returnValue
END
GO
ALTER TABLE [a]
ADD CONSTRAINT UOMGROUPIG
CHECK (your_schema_name.udf_Check1(UNITOFMEASURID) = 1)
GO
Here is the example: SQL Fiddle

Answer 2

You cannot write query within Check constraint. Instead you can call user defined function.
You can use same function in both constraints by passing #UOMGroupId value along with UNITOFMEASURID.
CREATE FUNCTION CheckFnctn(#UNITOFMEASURID int, #UOMGroupId int)
RETURNS int
AS
BEGIN
if exists(SELECT UnitOfMeasureId FROM b WHERE UOMGroupId=#UOMGroupId
and UnitOfMeasureId = #UNITOFMEASURID)
BEGIN
RETURN 1;
END
RETURN 0; --missed this line
END;
ALTER TABLE [a]
ADD CONSTRAINT UOMGROUPIG CHECK (dbo.CheckFnctn(UNITOFMEASURID, 1)=1);
ALTER TABLE [c]
ADD CONSTRAINT UOMGROUPIG CHECK (dbo.CheckFnctn(UNITOFMEASURID, 2)=1);