Database Engineering
  • Need of Database
  • Database and Database Management System
  • What is Relational Database Model ?
  • Installing Postgresql
    • Installing PostgreSQL on Linux
    • Installing PostgreSQL on Windows
    • Installing PostgreSQL on Mac
    • Postgres in Docker
  • What happens during the initial installation ?
    • Roles, Users & Groups
    • More examples on Roles
  • Sample Databases
    • DVD Rental Database
  • Querying Data
    • SELECT Query
    • Column Aliases
    • Order By
    • SELECT DISTINCT
    • DB-TASK-001
  • Filtering Data
    • WHERE ?
    • AND Operator
    • OR Operator
    • LIMIT
    • FETCH
    • IN
    • BETWEEN
    • LIKE
    • SIMILAR TO
    • IS NULL
    • ESCAPE
    • DB-TASK-002
  • Entity Relationship Diagram
    • What is an ER Diagram ?
    • Entity
    • Identifiers
    • Relationship
    • Attributes
    • Cardinality
    • Entity Relationship Diagram Tutorial
    • DB-TASK-003
  • Joins
    • Joins
    • Joins With Employee and Departments
  • Joins on E-Commerce
Powered by GitBook
On this page
  1. Filtering Data

FETCH

PreviousLIMITNextIN

Last updated 4 months ago

Introduction to PostgreSQL FETCH clause

To skip a certain number of rows and retrieve a specific number of rows, you often use the clause in the SELECT statement.

The LIMIT clause is widely used by many Relational Database Management Systems such as MySQL, H2, and HSQLDB. However, the LIMIT clause is not a SQL standard.

To conform with the SQL standard, PostgreSQL supports the FETCH clause to skip a certain number of rows and then fetch a specific number of rows.

Note that the FETCH clause was introduced as a part of the SQL standard in SQL:2008.

The following illustrates the syntax of the PostgreSQL FETCH clause

OFFSET row_to_skip { ROW | ROWS }
FETCH { FIRST | NEXT } [ row_count ] { ROW | ROWS } ONLY

  1. Skipping Rows (OFFSET):

    • The OFFSET keyword tells the database how many rows to skip before it starts showing results.

    • The number you provide (row_to_skip) must be a whole number (0 or more).

    • If you don’t provide a number, it will default to 0, meaning no rows will be skipped.

    • Example: If there are 10 rows and you skip 15, you’ll see no rows because you’ve skipped past all the data.

  2. Getting Rows (FETCH):

    • The FETCH keyword tells the database how many rows to return after skipping.

    • The number (row_count) must be 1 or more, and it defaults to 1 if you don’t provide it.

    • You can use FIRST or NEXT with ROW or ROWS (e.g., FETCH FIRST 3 ROWS is the same as FETCH NEXT 3 ROWS).

  3. Ordering Rows (ORDER BY):

    • Tables don’t store rows in a specific order, so results without an ORDER BY clause can appear in a random order.

    • Always use ORDER BY with FETCH to control which rows you get.

  4. Order of Clauses:

    • In SQL standards (like SQL:2008), OFFSET comes before FETCH.

    • PostgreSQL is flexible and allows you to write them in any order.

Example

SELECT * FROM employees
ORDER BY salary DESC
OFFSET 5 FETCH NEXT 3 ROWS;

  • Step 1: Sort employees by highest to lowest salary.

  • Step 2: Skip the first 5 employees.

  • Step 3: Show the next 3 employees.

If you skip ORDER BY, you might get a random set of rows, which could be confusing.

LIMIT