# Domain Relational Calculus in DBMS

**Domain Relational Calculus** is a non-procedural query language equivalent in power to Tuple Relational Calculus. Domain Relational Calculus provides only the description of the query but it does not provide the methods to solve it. In Domain Relational Calculus, a query is expressed as,

{ < x_{1}, x_{2}, x_{3}, ..., x_{n}> | P (x_{1}, x_{2}, x_{3}, ..., x_{n}) }

where, < x_{1}, x_{2}, x_{3}, …, x_{n} > represents resulting domains variables and P (x_{1}, x_{2}, x_{3}, …, x_{n} ) represents the condition or formula equivalent to the Predicate calculus.**Predicate Calculus Formula:**

- Set of all comparison operators
- Set of connectives like and, or, not
- Set of quantifiers

**Example:**

**Table-1: Customer**

Customer name | Street | City |
---|---|---|

Debomit | Kadamtala | Alipurduar |

Sayantan | Udaypur | Balurghat |

Soumya | Nutanchati | Bankura |

Ritu | Juhu | Mumbai |

**Table-2: Loan**

Loan number | Branch name | Amount |
---|---|---|

L01 | Main | 200 |

L03 | Main | 150 |

L10 | Sub | 90 |

L08 | Main | 60 |

**Table-3: Borrower**

Customer name | Loan number |
---|---|

Ritu | L01 |

Debomit | L08 |

Soumya | L03 |

**Query-1:** Find the loan number, branch, amount of loans of greater than or equal to 100 amount.

{≺l, b, a≻ | ≺l, b, a≻ ∈ loan ∧ (a ≥ 100)}

Resulting relation:

Loan number | Branch name | Amount |
---|---|---|

L01 | Main | 200 |

L03 | Main | 150 |

**Query-2:** Find the loan number for each loan of an amount greater or equal to 150.

{≺l≻ | ∃ b, a (≺l, b, a≻ ∈ loan ∧ (a ≥ 150)}

Resulting relation:

Loan number |
---|

L01 |

L03 |

**Query-3:** Find the names of all customers having a loan at the “Main” branch and find the loan amount .

{≺c, a≻ | ∃ l (≺c, l≻ ∈ borrower ∧ ∃ b (≺l, b, a≻ ∈ loan ∧ (b = “Main”)))}

Resulting relation:

Customer Name | Amount |
---|---|

Ritu | 200 |

Debomit | 60 |

Soumya | 150 |

**Note:**

The domain variables those will be in resulting relation must appear before | within ≺ and ≻ and all the domain variables must appear in which order they are in original relation or table.

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