The Basics of Inline View in Oracle

Summary: in this tutorial, you will learn about the inline view in Oracle and how to use it 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.

Here’s a basic SELECT statement:

SELECT column_list FROM table_name;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 that returns a result set in the FROM clause:

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.

Since 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.

In practice, you often use inline views to simplify complex queries by eliminating join operations or combining multiple queries into a single query.

Oracle inline view example #

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

Basic 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 ) FETCH NEXT 10 ROWS ONLY;Code language: SQL (Structured Query Language) (sql)

Try it

In this example:

• First, the inline view returns all products sorted by list prices in descending order.
• Then, the outer query retrieves the first 10 rows from the inline view.

Joining Inline Views with Tables #

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)

Try it

Output:

In this example:

• First, the inline view returns the category id list and the highest list price of the product in each category.
• Then, the outer query joins the inline view with the product_categories table to get the category name.

LATERAL inline views #

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 identifierCode language: SQL (Structured Query Language) (sql)

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

Fortunately, starting from Oracle 12c, you can use the LATERAL keyword to allow an inline view to reference the table on the left of the inline view definition in the FROM clause.

For 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)

Try it

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

Modifying Data with Oracle Inline Views #

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

Notice that the Playground does not support modifying the data via inline views.

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)

The following example deletes all video cards with a list price of 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)

Summary #

• An inline view is a subquery used in the FROM clause.