SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL, Second Edition

Summary

We began the chapter with a definition of the three types of subqueries defined by the SQL Standard—row, table, and scalar—and recalled that we had already covered how to use table subqueries in a FROM clause. We also briefly described the use of a row subquery and explained that not many commercial implementations support this yet.

Next, we showed how to use a subquery to generate a column expression in a SELECT clause. We discussed a simple example and then introduced two aggregate functions that are useful for fetching related summary information from another table. (We’ll cover all the aggregate functions in detail in the next chapter.)

We then discussed using subqueries to create complex filters in the WHERE clause. We first covered ...