Db2 LIMIT

Summary: in this tutorial, you will learn how to use the db2 LIMIT clause to limit the number of rows returned by a query.

Introduction to Db2 LIMIT clause

The LIMIT clause allows you to limit the number of rows returned by the query. The LIMIT clause is an extension of the SELECT statement that has the following syntax:

SELECT select_list
FROM table_name
ORDER BY sort_expression
LIMIT n [OFFSET m];

In this syntax:

• n is the number of rows to be returned.
• m is the number of rows to skip before returning the n rows.

Another shorter version of LIMIT clause is as follows:

LIMIT m, n;

This syntax means skipping m rows and returning the next n rows from the result set.

A table may store rows in an unspecified order. If you don’t use the ORDER BY clause with the LIMIT clause, the returned rows are also unspecified. Therefore, it is a good practice to always use the ORDER BY clause with the LIMIT clause.

Db2 LIMIT clause examples

We will use the books table from the sample database for the demonstration.

1) Db2 LIMIT OFFSET examples

The following query returns all rows from the books table sorted by titles:

SELECT 
    title, 
    rating
FROM 
    books
ORDER BY 
    title;

To get the first 10 books, you add the LIMIT clause to the above statement:

SELECT 
    title, 
    rating
FROM 
    books
ORDER BY 
    title
LIMIT
    10;

To skip the first 5 books and return the next 10 books, you use the LIMIT OFFSET clause as follows:

SELECT 
    title, 
    rating
FROM 
    books
ORDER BY 
    title
LIMIT 10 OFFSET 5;

Or in a shorter version:

SELECT 
    title, 
    rating
FROM 
    books
ORDER BY 
    title
LIMIT 5, 10;

2) Using Db2 LIMIT to get top-N rows

The LIMIT clause is useful to get the top-N report e.g., top 10 books that have the highest rating and top 20 books that have the highest number of pages.

This example uses the LIMIT clause to get the top 10 books that have the highest ratings:

SELECT 
    title, 
    rating
FROM 
    books
ORDER BY 
    rating DESC
LIMIT 10;

In this example:

• First, sort the books by rating from high to low using the ORDER BY clause
• Second, pick the first 10 rows from the sorted result set using the LIMIT clause.

In this tutorial, you have learned how to use the Db2 LIMIT clause to restrict the number of rows returned by a query.