JOINS(DISPLAYING DATA FROM MULTIPLE TABLES)

–Types of JOINS and its syntax

–Natural join:

•USING clause•ON clause

–Self-join

–Nonequijoins

–OUTER join:

•LEFT OUTER join•RIGHT OUTER join•FULL OUTER join

–Cartesian product

Cross join

Creating Natural Joins:

–The NATURAL JOIN clause is based on all columns in the two tables that have the same name.

–It selects rows from the two tables that have equal values in all matched columns.

If the columns having the same names have different data types, an error is returned.

RETRIEVING THE RECORDS WITH NATURAL JOIN

SELECT department_id, department_name,

       location_id, city

FROM   departments

NATURAL JOIN locations ;

Creating Joins with the USING Clause

–If several columns have the same names but the data types do not match, natural join can be applied using the USING clause to specify the columns that should be used for an equijoin.–Use the USING clause to match only one column when more than one column matches.–The NATURAL JOIN and USING clauses are mutually exclusive.

SELECT employee_id, last_name,

       location_id, department_id

FROM   employees JOIN departments

USING (department_id) 

Creating Joins with the ON Clause