**1 Answer**

written 8 months ago by |

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 |