Module 4: MySQL Joins and Set Operations

MySQL Joins and Set Operations

JOIN clause

is used to combine rows from two or more tables, based on a related column between them.

INNER JOIN

Returns records that have matching values in both tables

LEFT JOIN

Returns all records from the left table, and the matched records from the right table

RIGHT JOIN

Returns all records from the right table, and the matched records from the left table

CROSS JOIN

Returns all records from both tables

UNION operator

is used to combine the result-set of two or more SELECT statements.

• Every SELECT statement within UNION must have the same number of columns

• The columns must also have similar data types

• The columns in every SELECT statement must also be in the same order

UNION Syntax

SELECT column_name(s) FROM table1 UNION column_name(s) FROM table2;

• The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL:

SELECT column_name(s) FROM table1 UNION ALL column_name(s) FROM table2;