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Combining Queries
In this chapter, you’ll learn how to use the UNION operator to combine multiple SELECT statements into one result set.
Understanding Combined Queries
A SQL query usually contains a single SELECT statement that returns data from one or more tables. MySQL also enables you to perform multiple queries (multiple SELECT statements) and return the results as a single query result set. These combined queries are usually known as unions or compound queries.
There are basically two scenarios in which you’d use combined queries:
To return similarly structured data from different tables in a single query
To perform multiple queries against a single table and return the data as one query
Tip
Combining Queries and Multiple WHERE
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