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A subquery is a SELECT statement nested inside another statement such as SELECT, INSERT, UPDATE, or DELETE. Typically, you can use a subquery anywhere that you use an expression. Consider this following subquery example that uses the products table from the sample database.
This chapter contains these sections: About Queries and Subqueries. Creating Simple Queries. Hierarchical Queries. The Set Operators. Sorting Query Results. Joins. Using Subqueries. Unnesting of Nested Subqueries.
13 gru 2013 · When you use a subquery in a select clause, Oracle essentially treats it as a left join (you can see this in the explain plan for your query), with the cardinality of the rows being just one on the right for every row in the left.
This Oracle tutorial explains how to use Oracle subqueries with syntax and examples. A subquery is a query within a query. In Oracle, you can create subqueries within your SQL statements.
Using Subqueries. A subquery answers multiple-part questions. For example, to determine who works in Taylor's department, you can first use a subquery to determine the department in which Taylor works. You can then answer the original question with the parent SELECT statement.
13 wrz 2024 · Oracle supports several types of subqueries: single-row subqueries, multiple-row subqueries, correlated subqueries, scalar subqueries, and nested subqueries. Each serves different purposes, such as returning a single value or performing calculations based on data from the outer query.
Module 1. Introduction. This tutorial shows you how to write subqueries. It uses the bricks and colours table. Run the queries below to see their contents: select * from bricks; select * from colours; Note: This tutorial makes heavy use of group by. If you want a refresher on this, check out module 7 of Databases for Developers: Foundations.
