SQL JOIN is used to combine data from two or more different table based on a common field between them in a relational database.

There are 5 types of JOIN:

1. INNER JOIN
2. LEFT JOIN
3. RIGHT JOIN
4. FULL JOIN
5. CROSS JOIN

INNER JOIN: This SQL query returns all the common rows between the tables joined.

LEFT JOIN: This SQL query returns all the rows from the left table and the matched rows from the right table.

RIGHT JOIN: This SQL query returns all the rows from the right table and the matched rows from the left table.

FULL JOIN: This SQL query returns all the rows from both tables when there is a match in one of the tables.

FULL JOIN: This SQL query returns returns the Cartesian product of rows from tables in the join.

INNER JOIN SYNTAX:

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name=table2.column_name;

LEFT JOIN SYNTAX:

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name=table2.column_name;

RIGHT JOIN SYNTAX:

SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name=table2.column_name;

FULL JOIN SYNTAX:

SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;

CROSS JOIN SYNTAX:

SELECT column_name(s)
FROM table1 CROSS JOIN table2;