It is also possible to store some values produced by a query into variables—for instance, to reuse them later in other queries.
In this recipe, we will demonstrate this approach with a concrete example.
In the Controlling automatic database maintenance recipe of Chapter 9, Regular Maintenance, we will describe VACUUM, showing that it runs regularly on each table based on the number of rows that might need vacuuming (dead rows). The VACUUM command will run if that number exceeds a given threshold, which by default is just above 20% of the row count.
In this recipe, we will create a script that picks the table with the largest number of dead rows and runs VACUUM on it.