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What are fundamental relational algebra operations?
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1] Select. $(\sigma)$

2] Project. $(\pi)$

3] Set intersection. (n)

4] Natural join.

1] Select $(\sigma)$ - It is used to specify any condition on relation.

syntax

$\sigma$ condition (R)

condition is executed on relation R.

$\sigma$ sal>1000 (customer)

  • when this query is executed all customers whose salary is more than 1000 are displayed.

  • we can use >, <, >=, <=, <> operator for comparision.

we can combine two conditions with or (v) or AND (n) operator.

$\sigma$ ename = 'Rohit' ^ Sal > 10000 (customer)

2] Project. $(\pi)$ - It is used to display selected list of attribute of relation.

Syntax

$\pi$ <attribute list> (R)

eg. Consider

emp (emp no, name, email, salary)

example:

$\pi$ name, email (emp)

This will display employee name, email from emp table.

3] Set interaction (n) - This operation is used to find the common tuple from temp relation.

consider temp relations R & S.

R

A B
a 1
a 2
b 1

S

A B
a 2
b 3
b 1

R n S

A B
a 2
b 1

Natural Join:

This is binary operation and is message to join the temp relation having a common column, Both relations are joined based on common values.

R

A B
a 1
a 2
b 1

C

A B
a 2
b 3

R X C

A B A C
a 1 a 2
a 1 b 3
a 2 a 2
a 2 b 3
b 1 a 2
b 1 b 3
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