Most people do this by indenting the subquery in some way. In this case, we've used the name "sub."Ī quick note on formatting: The important thing to remember when using subqueries is to provide some way to for the reader to easily determine which parts of the query will be executed together. ![]() Subqueries are required to have names, which are added after parentheses the same way you would add an alias to a normal table. Once the inner query runs, the outer query will run using the results from the inner query as its underlying table: SELECT sub.* It might sound like a no-brainer, but it's important: your inner query must actually run on its own, as the database will treat it as an independent query. If you were to run this on its own, it would produce a result set like any other query. Let's break down what happens when you run the above query:įirst, the database runs the "inner query"-the part between the parentheses: SELECT * Here's an example of a basic subquery: SELECT sub.* Subqueries can be used in several places within a query, but it's easiest to start with the FROM statement. For example, if you wanted to take the sums of several columns, then average all of those values, you'd need to do each aggregation in a distinct step. Subqueries (also known as inner queries or nested queries) are a tool for performing operations in multiple steps. In this lesson, you will continue to work with the same San Francisco Crime data used in a previous lesson. ![]() Using subqueries to aggregate in multiple stages.Starting here? This lesson is part of a full-length tutorial in using SQL for Data Analysis.
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