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SQL - Self Joins

A SQL self join is used to join a table to itself, temporarily renaming one table, to compare records in the same table. The basic syntax joins the table to itself using aliases, specifying a common field in the WHERE clause. An example joins a CUSTOMERS table to itself to return records where the SALARY is less than another record's SALARY, producing all combinations that meet the criteria.

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Pratik Deshmukh
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815 views2 pages

SQL - Self Joins

A SQL self join is used to join a table to itself, temporarily renaming one table, to compare records in the same table. The basic syntax joins the table to itself using aliases, specifying a common field in the WHERE clause. An example joins a CUSTOMERS table to itself to return records where the SALARY is less than another record's SALARY, producing all combinations that meet the criteria.

Uploaded by

Pratik Deshmukh
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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9/6/21, 2:04 PM SQL - SELF JOINS

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_field = b.common_field;

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

Example
Consider the following table.
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 the following result −

+----+----------+---------+

| ID | NAME | SALARY |

+----+----------+---------+

| 2 | Ramesh | 1500.00 |

https://www.tutorialspoint.com/sql/sql-self-joins.htm 1/2
9/6/21, 2:04 PM SQL - SELF JOINS

| 2 | kaushik | 1500.00 |

| 1 | Chaitali | 2000.00 |

| 2 | Chaitali | 1500.00 |

| 3 | Chaitali | 2000.00 |

| 6 | Chaitali | 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 |

+----+----------+---------+

https://www.tutorialspoint.com/sql/sql-self-joins.htm 2/2

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