The SQL JOIN statement is used to combine the data contained in two relational database tables based upon a common attribute.
Types of Join:
- Inner Join
- Outer Join
- Left Outer Join
- Right Outer Join
- Full Outer Join
- Cross Join
1. Inner Join: Inner Join is a default type join of SQL Server. It uses logical operators such as =, <, > to match the records in two tables. Inner Join includes equi join and natural joins.
Self Join: Self join joins a single sql database table to itself.
Equi Join: Equi Join returns all the columns from both tables and filters the records satisfying the matching condition specified in Join “ON” statement of sql inner join query.
2. Outer Join: Outer Join has further 3 sub categories as left, right and full. Outer Join uses these category names as keywords that can be specified in the FROM clause.
o Left Outer Join: Left Outer Join returns all the rows from the table specified first in the Left Outer Join Clause. If in the left table any row has no matching record in the right side table then that row returns null column values for that particular tuple.
o Right Outer Join: Right Outer Join is exactly the reverse method of Left Outer Join. It returns all the rows from right table and returns null values for the rows having no match in the left joined table.
o Full Outer Join: Full outer join returns all the rows from both left and right joined tables. If there is any match missing from the left table then it returns null column values for left side table and if there is any match missing from right table then it returns null value columns for the right side table.
2. Cross Join: Cross join works as a Cartesian product of rows for both left and right table. It combined each row of left table with all the rows of right table.