What is a join? Explain different types of joins?

Answer Posted / nareshkumar

A join is a condition that links the data in seperate but
related tables. The tables usually have a parent-child
relationship. If a query does not contain a join, the
database returns a result set that contains all possible
combinations of the rows in the query tables.

Types of joins:

1) Equi-Joins
Link tables based on the equality between the values in the
column of one table and the values in the column of another.

2) Theta Joins
Link tables based on a relationship other than equality
between two columns.

3) Outer Joins (Left Outer, Right Outer, Full Outer)
Link two tables, one of which has rows that do not match
those in the common column of the other table.

4) Shortcut Joins
Join providing an alternative path between two tables,
bypassing intermediate tables, leading to the same result,
regardless of direction. Optimizes query time by cutting
long join paths as short as possible.

5) Self restricting joins
Single table join used to set a restriction on the table.

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