What is SELF JOIN and when would you use it?

• The SQL SELF JOIN is used to join a table to itself
• You use a self join when a table references data in itself.
• SQL self-join simply is a normal join which is used to join a table to itself.

Example:

SELECT a.column_name, b.column_name...

FROM table1 a,table1 b

WHERE a.common_field = b.common_field;