Compare SQL Server Datasets with INTERSECT and EXCEPT

Problem

When joining multiple datasets you have always had the ability to use the UNION and UNION ALL operator to allow you to pull a distinct result set (union) or a complete result set (union all). These are very helpful commands when you need to pull data from different tables and show the results as one unified distinct result set. On the opposite side of this it would be helpful to only show a result set where both sets of data match or only where data exists in one of the tables and not the other. This could be done with using different join types, but what other options does SQL Server offer?

Solution

With SQL Server, Microsoft introduced the INTERSECT and EXCEPT operators to further extend what you could already do with the UNION and UNION ALL operators.

INTERSECT – gives you the final result set where values in both of the tables match
EXCEPT – gives you the final result set where data exists in the first dataset and not in the second dataset

The advantage of these commands is that it allows you to get a distinct listing across all of the columns such as the UNION and UNION ALL operators do without having to do a group by or do a comparison of every single column.

Like the UNION and UNION ALL operators the table structures need to be consistent as well as the columns need to have compatible data types.

Let’s take for example we have two tables manager and customer. Both of these tables have somewhat the same structure such as the following columns:

FirstName
LastName
AddressLine1
City
StateProvinceCode
PostalCode

Here is the Manager table sample data:

Here is the Customer table sample data:

We want to do two queries:

Find the occurrences where a manager is a customer (intersect)
Find the occurrences where the manager is not a customer (except)

SQL Server INTERSECT Examples

If we want to find out which people exist in both the customer table and the manager table and get a distinct list back we can issue the following command:

SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   MANAGER 
INTERSECT  
SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   CUSTOMER

Here is the result set:

To do this same thing with a regular T-SQL command we would have to write the following:

SELECT   M.FIRSTNAME, 
         M.LASTNAME, 
         M.ADDRESSLINE1, 
         M.CITY, 
         M.STATEPROVINCECODE, 
         M.POSTALCODE 
FROM     MANAGER M 
         INNER JOIN CUSTOMER C 
           ON M.FIRSTNAME = C.FIRSTNAME 
              AND M.LASTNAME = C.LASTNAME 
              AND M.ADDRESSLINE1 = C.ADDRESSLINE1 
              AND M.CITY = C.CITY 
              AND M.POSTALCODE = C.POSTALCODE 
GROUP BY M.FIRSTNAME,M.LASTNAME,M.ADDRESSLINE1,M.CITY, 
         M.STATEPROVINCECODE,M.POSTALCODE

SQL Server EXCEPT Examples

If we want to find out which people exists in the manager table, but not in the customer table and get a distinct list back we can issue the following command:

SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   MANAGER  
EXCEPT 
SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   CUSTOMER

Here is the result set:

To do this same thing with a regular T-SQL command we would have to write the following:

SELECT   M.FIRSTNAME, 
         M.LASTNAME, 
         M.ADDRESSLINE1, 
         M.CITY, 
         M.STATEPROVINCECODE, 
         M.POSTALCODE 
FROM     MANAGER M 
WHERE    NOT EXISTS (SELECT * 
                     FROM   CUSTOMER C 
                     WHERE  M.FIRSTNAME = C.FIRSTNAME 
                            AND M.LASTNAME = C.LASTNAME 
                            AND M.ADDRESSLINE1 = C.ADDRESSLINE1 
                            AND M.CITY = C.CITY 
                            AND M.POSTALCODE = C.POSTALCODE) 
GROUP BY M.FIRSTNAME,M.LASTNAME,M.ADDRESSLINE1,M.CITY, 
         M.STATEPROVINCECODE,M.POSTALCODE

From the two examples above we can see that using the EXCEPT and INTERSECT commands are much simpler to write then having to write the join or exists statements.

To take this a step further if we had a third table (or forth…) that listed sales reps and we wanted to find out which managers were customers, but not sales reps we could do the following.

Here is the SalesRep table sample data:

SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   MANAGER 
INTERSECT  
SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   CUSTOMER  
EXCEPT 
SELECT FIRSTNAME, 
       LASTNAME, 
       ADDRESSLINE1, 
       CITY, 
       STATEPROVINCECODE, 
       POSTALCODE 
FROM   SALESREP

Here is the result set:

As you can see this is pretty simple to mix and match these statements. In addition, you could also use the UNION and UNION ALL operators to further extend your final result sets.

Next Steps

Take a look at your existing code to see how the INTERSECT and EXCEPT operators could be used
Keep these new operators in mind next time you need to compare different datasets with like data

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