SQL SELF JOIN

It is where a table is joined to itself assuming the tables are 2 tables with temporarily renaming one table in SQL query.

For example EMPLOYEE Table has

EMP_IDEMP_NAMEHIRE_DATESALARYDEPT_ID
1Roger Fed2001-05-0150004
2Djoker Nova2002-07-1565001
3Stef Graph2005-10-1880005
4Mart Hingis2007-01-0372003
5Andre Duplesi2008-06-245600null

Now lets write SELF JOIN query:

SELECT , E.EMP_NAME, E.SALARY , F.HIRE_DATE

FROM EMPLOYEE E, EMPLOYEE F

WHERE E.SALARY < F.SALARY;

The Output will look like this:

emp_namesalaryhire_date
Roger Fed50002002-07-15
Roger Fed50002005-10-18
Roger Fed50002007-01-03
Roger Fed50002008-06-24
Roger Fed50002009-04-01
Roger Fed50002011-04-13
Djoker Nova65002005-10-18
Djoker Nova65002007-01-03
Mart Hingis72002005-10-18
Andre Duplesi56002002-07-15

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