SQL: Derived Relations

SQL-92 allows a subquery expression to be used in the from clause.

If such an expression is used, the result relation must be given a name, and the attributes can be renamed.

Find the average account balance of those branches where the average account balance is greater than $1,000.

 select bname, avg-balance

             from (select bname, avg(balance)

                                           from account

                                           group by bname)

                                           as result(bname, avg-balance)

where avg-balance > 1000