Join is a query that is used to combine rows from two or more tables, views, or materialized views. It retrieves data from multiple tables and creates a new table.
INNER JOIN
Inner Join is the simplest and most common type of join. It is also known as simple join. It returns all rows from multiple tables where the join condition is met.
Syntax:
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column; Example:
SELECT *
FROM students
INNER JOIN admission
ON students.student_id = admission.student_id;
Above Query join both table and print all rows which statisfy given codintion.
OUTER JOIN
It is categorized in Left Outer Join, Right Outer Join and Full Outer Join by Oracle 9i ANSI/ISO 1999 standard.Left Outer Join
Left Outer Join returns all rows from the left (first) table specified in the ON condition and only those rows from the right (second) table where the join condition is met.
Syntax:
SELECT columns
FROM table1
LEFT [OUTER] JOIN table2
ON table1.column = table2.column; Example:
SELECT *
FROM department
LEFT OUTER JOIN admission
ON department.dept_id = admission.dept_id; 
Right Outer Join
The Right Outer Join returns all rows from the right-hand table specified in the ON condition and only those rows from the other table where the join condition is met.
Syntax
SELECT columns
FROM table1
RIGHT [OUTER] JOIN table2
ON table1.column = table2.column; Example:
SELECT *
FROM department
RIGHT OUTER JOIN admission
ON department.dept_id = admission.dept_id; 
Full Outer Join
The Full Outer Join returns all rows from the left hand table and right hand table. It places NULL where the join condition is not met.
Syntax
SELECT columns
FROM table1
FULL [OUTER] JOIN table2
ON table1.column = table2.column; Example:
SELECT *
FROM department
FULL OUTER JOIN admission
ON department.dept_id = admission.dept_id; 
EQUI JOIN
Oracle Equijoin returns the matching column values of the associated tables. It uses a comparison operator in the WHERE clause to refer equality.
Syntax
SELECT column_list
FROM table1, table2....
WHERE table1.column_name =
table2.column_name; Alternative:
Equijoin also can be performed by using JOIN keyword followed by ON keyword and then specifying names of the columns along with their associated tables to check equality.
Syntax
SELECT *
FROM table1
JOIN table2
[ON (join_condition)] Example:
SELECT *
FROM department
JOIN admission
ON department.dept_id = admission.dept_id; SELECT *
FROM department, admission
WHERE department.dept_id = admission.dept_id; 
SELF JOIN
Self Join is a specific type of Join. In Self Join, a table is joined with itself (Unary relationship). A self join simply specifies that each rows of a table is combined with itself and every other row of the table.
Syntax
SELECT a.column_name, b.column_name...
FROM table1 a, table1 b
WHERE a.common_filed = b.common_field;
Example
SELECT *
FROM students a,students b
WHERE a.dob = b.dob;
Cross Join (Cartesian Products)
The CROSS JOIN specifies that all rows from first table join with all of the rows of second table.
If there are "x" rows in table1 and "y" rows in table2 then the cross join result set have x*y rows. It normally happens when no matching join columns are specified.In simple words you can say that if two tables in a join query have no join condition, then the Oracle returns their Cartesian product.
Syntax
SELECT *
FROM table1
CROSS JOIN table2; Or
SELECT * FROM table1, table2
Both the above syntax are same and used for Cartesian product. They provide similar result after execution.
Example:
SELECT *
FROM department,admission;It will return catesian product.