Unique constraint is a type of column restriction within a table that dictates that all values in that column must be unique though may be null. A UNIQUE constraint is used to enforce the uniqueness of values in a column or in a set of columns in a particular table – that is, for columns that are not included in the table’s primary key set. A UNIQUE constraint dictates that a column must not store duplicate values.
A unique constraint is used to ensure that the data stored in a column or set of columns is unique across the entire table. This means that no two rows can have the same value for the specified column or columns.
Unique constraints are used to ensure data integrity and consistency. They prevent duplicate data from being entered into tables and help maintain data accuracy. Unique constraints are also used to enforce business rules and ensure that data is entered correctly.
Unique constraints can be referenced by a FOREIGN KEY constraint. When a UNIQUE constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure all values are unique.
In summary, Unique constraints are used to ensure that data stored in a column or set of columns is unique across the entire table. They help maintain data accuracy and integrity by preventing duplicate data from being entered into tables.
Here are some websites that discuss What Is The Function Of The Unique Constraint:
- https://www.techopedia.com/definition/24478/unique-constraint
- https://learnsql.com/blog/unique-constraint-in-sql/
- https://learn.microsoft.com/en-us/sql/relational-databases/tables/unique-constraints-and-check-constraints?view=sql-server-ver16
- https://www.w3schools.com/sqL/sql_unique.asp
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