Creating Combined Queries
SQL queries are combined using the UNION operator. Using UNION, multiple SELECT statements can be specified, and their results can be combined into a single result set.
Using UNION is simple enough. All you do is specify each SELECT statement and place the keyword UNION between each.
Let's look at an example. You need a report on all your customers in Illinois, Indiana, and Michigan. You also want to include all Fun4All locations, regardless of state. Of course, you can create a WHERE clause that will do this, but this time you'll use a UNION instead.
As I just explained, creating a UNION involves writing multiple SELECT statements. First look at the individual statements:
SELECT cust_name, cust_contact, ...