What are Various kind of join Operations?

A join combines records from two or more tables in a relational database. In the Structured Query Language (SQL), there are three types of joins: inner, outer, and cross. Outer joins are subdivided further into left outer joins, right outer joins, and full outer joins.
Join Forms
Inner join
An inner join essentially finds the intersection between the two tables. This is the most common type of join used, and is considered the default join type. The join example below takes all the records from table A (in this case, employee) and finds the matching record(s) from table B (department). If no match is found, the record from A is not included in the results. If multiple results are found in B that match the predicate then one row will be returned for each (the values from A will be repeated).
Special care must be taken when joining tables on columns that can be NULL since NULL values will never match each other. See Left Outer Join or Right Outer Join for a solution.
Left outer join
A left outer join is very different from an inner join. Instead of limiting results to those in both tables, it limits results to those in the "left" table (A). This means that if the ON clause matches 0 records in B, a row in the result will still be returned—but with NULL values for each column from B.
It returns all the values from left table + ( (matched values from right table) OR (null when the values from the right don't match) ).
For example, this allows us to find the employee's departments, but still show the employee even when their department is NULL or does not exist. The example above would have ignored employees in non-existent departments.
Right outer join
A right outer join is much like a left outer join, except that the tables are reversed. Every record from the right side, B or department, will be returned, and NULL values will be returned for those that have no matching record in A.
It returns all the values from right table + matched values from left table (OR null)
Full outer join
A full outer join combines the results of both left and right outer joins. These joins will show records from both tables, and fill in NULLs for missing matches on either side.
Some database systems do not support this functionality, but it can be emulated through the use of left and right outer joins and unions (see below).
Cross join
While not used very commonly, a cross join is the foundation upon which inner joins are built. A cross join returns the cartesian product of the sets of rows from the joined tables.
The SQL code for a cross join lists the tables to be joined (FROM), but does not include any filtering predicate (WHERE).