Discuss Equijoin & Natural Join with examples.

Discuss Equijoin & Natural Join with examples.

Answer:-

1. Equi Join

Definition:

• An Equi Join is a type of inner join that combines rows from two or more tables based on a condition that compares columns using an equality operator (=).
• It requires you to explicitly specify the join condition.

Example:

Assume we have the following tables:

Sailors(sid, sname, rating, age)
Reserves(sid, bid, day)

Query using Equi Join:

SELECT Sailors.sid, sname, rating, age, bid, day
FROM Sailors
JOIN Reserves ON Sailors.sid = Reserves.sid;

Key Point:

• You must specify the column to join on.
• If columns have the same name, both are retained in the result unless selected specifically.

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2. Natural Join

Definition:

• A Natural Join automatically joins tables based on all columns with the same names in both tables.
• It removes duplicate columns from the result.

Example:

Using the same tables:

SELECT *
FROM Sailors
NATURAL JOIN Reserves;

Key Point:

• Joins on the common column(s) sid automatically.
• No need to write an explicit condition.
• Removes duplicate sid from output.

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Comparison Table

Feature	Equi Join	Natural Join
Join Condition	Must be written explicitly (ON A.col = B.col)	Implicit (based on same-named columns)
Duplicate Columns	Keeps duplicates unless handled manually	Automatically removes duplicates
Flexibility	More control (custom join conditions)	Less control, but cleaner for simple joins