SQL JOINS

SQL Join is used to fetch data from two or more tables, which is joined to appear as single set of data. SQL Join is used for combining column from two or more tables by using values common to both tables.

Join Keyword is used in SQL queries for joining two or more tables.

Types of Join

• Inner
• Outer
• Left
• Right

• 

Student

Reg_id	name	address	sub_id
2008/SP/67	Thenuzan	Kurumankadu	CSC
2008/SP/20	Nilashan	Poonthodam	CSC
2008/SP/41	Tharopan	Chunaakam	PHY
2008/SP/34	Pancha	Vadukkoodai	PHY

Subject

sub_id	sub_name
CSC	Computer Science
PHY	Physics
CHE	Chemistry

CROSS JOIN /Cartesian Product
This type of JOIN returns the cartesian product of rows of from the tables in Join. It will return a table which consists of records which combines each row from the first table with each row of the second table.

SELECT column-name-list
from tableA
CROSS JOIN
tableB;

SELECT *
from Student
CROSS JOIN
Subject

Reg_id	name	address	sub_id	sub_id	sub_name
2008/SP/67	Thenuzan	Kurumankadu	CSC	CSC	Computer Science
2008/SP/67	Thenuzan	Kurumankadu	CSC	PHY	Physics
2008/SP/67	Thenuzan	Kurumankadu	CSC	CHE	Chemistry
2008/SP/20	Nilashan	Poonthodam	CSC	CSC	Computer Science
2008/SP/20	Nilashan	Poonthodam	CSC	PHY	Physics
2008/SP/20	Nilashan	Poonthodam	CSC	CHE	Chemistry

INNER JOIN
The INNER JOIN selects all rows from both participating tables as long as there is a match between the columns. An SQL INNER JOIN is same as JOIN clause, combining rows from two or more tables. 

SELECT * 
FROM tableA INNER JOIN tableB 
ON tableA.column_name = tableB.column_name;