Sams Teach Yourself SQL in 24 Hours, Third Edition By Ronald R. Plew, Ryan K. Stephens
Table of Contents
Hour 15. Combining Multiple Queries into One
Compound operators are used to combine and restrict the results of two SELECT statements. These operators can be used to return or suppress the output of duplicate records. Compound operators can bring together similar data that is stored in different fields.
Compound queries allow you to combine the results of more than one query to return a single set of data. Compound queries are often simpler to write than a single query with complex conditions. Compound queries also allow for more flexibility regarding the never-ending task of data retrieval.
