The Basics of Inline View in Oracle

Summary: in this tutorial, you will learn about the inline view in Oracle and how to use them to simplify complex queries or condense several separate queries into one.

Introduction to the inline view in Oracle

An inline view is not a real view but a subquery in the FROM clause of a SELECT statement. Consider the following SELECT statement:

SELECT column_list FROM table;
Code language: SQL (Structured Query Language) (sql)

In the FROM clause, you can specify a table from which you want to query data. Besides a table, you can use a subquery as shown in the following example:

SELECT column_list FROM ( SELECT * FROM table_name ) t;
Code language: SQL (Structured Query Language) (sql)

The subquery specified in the FROM clause of a query is called an inline view. Because an inline view can replace a table in a query, it is also called a derived table. Sometimes, you may hear the term subselect, which is the same meaning as the inline view.

You often use the inline view in Oracle to simplify complex queries by eliminating join operations or condensing separate queries into a single query.

Oracle inline view example

Let’s use the products table in the sample database for the demonstration.

products table

A) simple Oracle inline view example

The following query retrieves the top 10 most expensive products from the products table:

SELECT * FROM ( SELECT product_id, product_name, list_price FROM products ORDER BY list_price DESC ) WHERE ROWNUM <= 10;
Code language: SQL (Structured Query Language) (sql)
oracle inline view example

In this example, first, the inline view returns all products sorted by list prices in descending order. And then the outer query retrieves the first 10 rows from the inline view.

B) Inline view joins with a table example

The following example joins an inline view with a table in the FROM clause. It returns the product categories and the highest list price of products in each category:

SELECT category_name, max_list_price FROM product_categories a, ( SELECT category_id, MAX( list_price ) max_list_price FROM products GROUP BY category_id ) b WHERE a.category_id = b.category_id ORDER BY category_name;
Code language: SQL (Structured Query Language) (sql)
oracle inline view and join

In this example, the inline view returns the category id list and the highest list price of product in each category. The outer query joins the inline view with the product_categories table to get the category name.

C) LATERAL inline view example

Consider the following statement:

SELECT category_name, product_name FROM products p, ( SELECT * FROM product_categories c WHERE c.category_id = p.category_id ) ORDER BY product_name;
Code language: SQL (Structured Query Language) (sql)

Oracle issued an error:

ORA-00904: "P"."CATEGORY_ID": invalid identifier
Code language: SQL (Structured Query Language) (sql)

This is because the inline view cannot reference the tables from the outside of its definition.

Fortunately, since Oracle 12c, by using the LATERAL keyword, an inline view can reference the table on the left of the inline view definition in the FROM clause as shown in the following example:

SELECT product_name, category_name FROM products p, LATERAL( SELECT * FROM product_categories c WHERE c.category_id = p.category_id ) ORDER BY product_name;
Code language: SQL (Structured Query Language) (sql)
oracle inline view - LATERAL

Note that the LATERAL inline views are subject to some restrictions listed in the documentation.

D) Oracle inline view: data manipulation examples

You can issue data manipulation statement such as INSERT, UPDATE, and DELETE against updatable inline view.

For example, the following statement increases the list prices of CPU products by 15%:

UPDATE ( SELECT list_price FROM products INNER JOIN product_categories using (category_id) WHERE category_name = 'CPU' ) SET list_price = list_price * 1.15;
Code language: SQL (Structured Query Language) (sql)

And the following example deletes all video cards with the list price less than 1,000:

DELETE ( SELECT list_price FROM products INNER JOIN product_categories USING(category_id) WHERE category_name = 'Video Card' ) WHERE list_price < 1000;
Code language: SQL (Structured Query Language) (sql)

In this tutorial, you have learned about the inline view in Oracle to simplify complex queries and condense several separate queries into one query.

Was this tutorial helpful?