Sams Teach Yourself SQL in 24 Hours, Fifth Edition

Hour 15. Combining Multiple Queries into One

What You’ll Learn in This Hour:

• An overview of the operators that combine queries

• When to use the commands to combine queries

• Using the GROUP BY clause with the compound operators

• Using the ORDER BY clause with the compound operators

• How to retrieve accurate data

In this hour, you learn how to combine SQL queries by using the UNION, UNION ALL, INTERSECT, and EXCEPT operators. Once again, you must check your particular implementation for any variations in the use of these operators.

Single Queries Versus Compound Queries

The single query is one SELECT statement, whereas the compound query includes two or more SELECT statements.

You form compound queries by using some type of operator to ...