Web | This Site

Learning Basic SQL
Advanced SQL
SQL Functions
SQL Useful Resources
Selected Reading
© 2011 TutorialsPoint.COM

| Home |  | References |  | Discussion Forums |  | About TP

# SQL - SELF JOINS

The SQL SELF JOIN is used to join a table to itself, as if the table were two tables, temporarily renaming at least one table in the SQL statement.

# Syntax:

The basic syntax of SELF JOIN is as follows:

    SELECT a.column_name, b.column_name...
    FROM table1 a, table1 b
    WHERE a.common_filed = b.common_field;

Here WHERE clause could be any given expression based on your requirement.

# Example:

Consider following two tables, (a) CUSTOMERS table is as follows:

    +----+----------+-----+-----------+----------+
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
    |  3 | kaushik  |  23 | Kota      |  2000.00 |
    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  6 | Komal    |  22 | MP        |  4500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+

Now let us join this table using SELF JOIN as follows:

    SQL> SELECT  a.ID, b.NAME, a.SALARY
         FROM CUSTOMERS a, CUSTOMERS b
         WHERE a.SALARY < b.SALARY;

This would produce following result:

    +----+---------+---------+
    | ID | NAME    | SALARY  |
    +----+---------+---------+
    |  2 | Ramesh  | 1500.00 |
    |  2 | kaushik | 1500.00 |
    |  1 | kaushik | 2000.00 |
    |  2 | kaushik | 1500.00 |
    |  3 | kaushik | 2000.00 |
    |  6 | kaushik | 4500.00 |
    |  1 | Hardik  | 2000.00 |
    |  2 | Hardik  | 1500.00 |
    |  3 | Hardik  | 2000.00 |
    |  4 | Hardik  | 6500.00 |
    |  6 | Hardik  | 4500.00 |
    |  1 | Komal   | 2000.00 |
    |  2 | Komal   | 1500.00 |
    |  3 | Komal   | 2000.00 |
    |  1 | Muffy   | 2000.00 |
    |  2 | Muffy   | 1500.00 |
    |  3 | Muffy   | 2000.00 |
    |  4 | Muffy   | 6500.00 |
    |  5 | Muffy   | 8500.00 |
    |  6 | Muffy   | 4500.00 |
    +----+---------+---------+

Advertisement

Online Image Processing

Indian Baby Names