PostgreSQL - LIMIT with OFFSET clause

The PostgreSQL LIMIT clause is a powerful feature that allows users to retrieve a specific subset of rows from query results. This optional clause can be paired with the OFFSET clause to skip a specified number of rows before returning the desired results. Such functionality is particularly beneficial for pagination, enabling us to fetch data in manageable chunks.

In this article, we will explain the PostgreSQL LIMIT and OFFSET clauses in-depth, with practical examples and outputs to illustrate their application.

PostgreSQL LIMIT with OFFSET Clause

The LIMIT clause restricts the number of rows returned by a PostgreSQL query. By specifying a number after the LIMIT keyword, we train PostgreSQL to return only that many rows. This is particularly advantageous when working with large tables where retrieving every row could lead to performance issues, increased loading times, and an overcrowded user interface.

Syntax

SELECT * FROM table LIMIT n OFFSET m;

Key Terms

• The LIMIT clause returns a subset of "n" rows from the query result.
  
• The OFFSET clause placed after the LIMIT clause skips "m" number of rows before returning the result query.
  
• If "m" is Zero, then it acts as a normal LIMIT clause.

PostgreSQL LIMIT with OFFSET Clause Examples

Now, let us examine a few practical examples of using the LIMIT and OFFSET clauses in PostgreSQL to better understand their application. PostgreSQL LIMIT with OFFSET clause examples provide valuable insights into how to efficiently manage large datasets and implement pagination in our queries

Example 1: Fetching Films with LIMIT and OFFSET

Here we will query for 5 films starting from the seventh one ordered by 'film_id' from the 'film' table of our sample database.

Query:

SELECT
    film_id,
    title,
    release_year
FROM
    film
ORDER BY
    film_id
LIMIT 5 OFFSET 6;

Output

Explanation:

This query retrieves 5 films starting from the seventh record (offset 6) in the table, ordered by their 'film_id'.

Example 2: Fetching Films Ordered by Title in Descending Order

Here we will query for 5 films starting from the seventh one ordered by 'film_id' from the film table of our sample database in descending order of the film 'title'.

Query:

SELECT
    film_id,
    title,
    release_year
FROM
    film
ORDER BY
    title DESC
LIMIT 5 OFFSET 6;

Output

Explanation:

This query retrieves 5 films starting from the seventh record (offset 6) in the table, ordered by their 'title' in descending order.

Important Points About PostgreSQL LIMIT with OFFSET Clause

• The LIMIT clause restricts the number of rows returned by a query. The OFFSET clause skips a specified number of rows before beginning to return rows from the query.
  
• An OFFSET of zero (OFFSET 0) effectively ignores the OFFSET clause, making the query act as a standard LIMIT query.
  
• LIMIT and OFFSET are commonly used for pagination in applications, allowing users to retrieve data in smaller, manageable chunks.
  
• An alternative to LIMIT and OFFSET is keyset pagination, which uses a WHERE clause to filter rows based on a specific key.
  
• PostgreSQL also supports the FETCH clause as an alternative to LIMIT, which can be more readable in some contexts.

Conclusion

Understanding the LIMIT and OFFSET clauses in PostgreSQL is important for effective data retrieval, especially when working with large datasets. By utilizing these clauses, you can implement efficient pagination strategies in your applications, enhancing the overall user experience. Whether we are fetching a limited number of results or skipping records, mastering the use of LIMIT and OFFSET can significantly improve our SQL querying capabilities.