SQL Constraints, NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK, DEFAULT, CREATE INDEX

SQL Constraints

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Constraints

  |

  |- CHECK

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  |- NOT NULL

  |

  |- UNIQUE

  |

  |- PRIMARY KEY

  |

  |- DEFAULT

  |

  |- FOREIGN KEY

  |

  |- INDEX

* These constraints are also known as Integrity Constraints.

* SQL Constraints:- Constraints are the rules and restrictions applied to the data in a table.

* NOT NULL:- Value cannot be Null in a column.

* UNIQUE:- Value cannot be the same in a column.

* PRIMARY KEY:- Used to uniquely identify a row.

* FOREIGN KEY:- References a row in another table.

* CHECK:- Satisfies a specific condition.

* DEFAULT:- Set default value.

* CREATE INDEX:- Used to speed up the reading process.