Sams Teach Yourself SQL in 10 Minutes

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

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, ...