Constraints ensures valid data values are entered in column and that the value are entered in a column and that relationship between tables are maintained.
Various types of Constraints:-
- Domain Integrity
- Referential Integrity
- Entity Integrity
Domain Integrity:-
- Default Constraints
- Check Constraints
- Foreign Key Constraints
- Null Constraints
Default Constraints;- Specifies the default value for the column when an Insert statement does not provide a value.
Check Constraints:- Specifies that data values that are accepatable in a column.
Foreign Key Constraints:- Specifies the data values that are acceptable to update based on values in a column in a another table.
Null Constraints:- Specifies whether the value of a column can be null.
Referential Integrity:-
- Primary Key Constraints
- Unique Constraints
Primary Key Constraints:-It identifies each row uniquely. It ensures, that users do not enter duplicate values and that Index is created to enhance the performance. Null values are not allowed.
Unique Constraints:- It prevents duplicate of alternate keys and ensures that an Index is created to enhance the performance. Null values are allowed.
Entity Integrity:-
- Foreign Key Constraints
- Check Constraints
Foreign Key Constraints:- Defines a column or combination of columns with values that match the Primary Key of the same or another table.
Check Constraints:- Specifies the data values that are acceptable in a column based on values in other columns in the table.
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