Verify unique record in SQL server 2012

Question

I would like verify unique record in customer table and write the following query

declare @NT1 int

set @NT1 = (SELECT LogID, CustomerID, count(1)
FROM dbo.Customer
group by LogID,CustomerID
having count(1) >1)

if @NT1 > 1

print 'Fail'

ELSE  
    PRINT 'Pass';

I get the following message when run the query:

Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.

Answer 1

If you want to verify that no (LogId, CustomerId) pair occurs more than once in the Customer table, then you can do that.

The simplest way is:

create unique index idxu_customer_logid_customerid on customer(logid, customerid);

That way, the database ensures uniqueness. And, the rest of your code doesn't have to worry about it.

If you want to run your test, use exists :

IF (EXISTS (SELECT LogID, CustomerID, count(1)
            FROM dbo.Customer
            GROUP BY LogID, CustomerID
            HAVING count(1) > 1
           )
   )
BEGIN
    PRINT 'Fail';
END
ELSE 
BEGIN 
    PRINT 'Pass';
END;

Answer 2

DECLARE @Ncount int

set @Ncount =  (select top 1 
 count(1) 
            FROM dbo.Customer
            GROUP BY LogID, CustomerID
                        HAVING count(1) > 0
           )

SELECT IIF ( @Ncount >= 1, 'Failed', 'Pass' ) AS Result;