Unique Constraint

Unique Constraint

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A unique constraint is a database constraint that ensures the uniqueness of values in a specific column or combination of columns within a table. It prevents duplicate or repeated values from being inserted into the specified columns, thereby enforcing data integrity and maintaining data consistency.

Here are some key points about unique constraints:

  1. Uniqueness: A unique constraint guarantees that every value in the specified column(s) is unique within the table. No two rows can have the same value(s) for the column(s) defined in the constraint.
  2. Data Integrity: By enforcing uniqueness, a unique constraint helps maintain data integrity by preventing the insertion of duplicate or redundant data. It ensures that each row in the table has a distinct value or combination of values in the specified column(s).
  3. Table-level or Column-level: Unique constraints can be defined at the table level or column level. A table-level unique constraint applies to the entire table, ensuring the uniqueness of the specified column(s) across all rows. A column-level unique constraint applies to a specific column, ensuring the uniqueness of values within that column only.
  4. Automatic Indexing: In many database systems, a unique constraint is automatically indexed to optimize the performance of unique value searches. This index allows for efficient retrieval and comparison of values to enforce uniqueness.
  5. Multiple Columns: Unique constraints can involve a single column or a combination of multiple columns. In the case of multi-column unique constraints, the combination of values in the specified columns must be unique for each row.
  6. Error Handling: When an attempt is made to insert a duplicate value that violates a unique constraint, the database system throws an error, typically referred to as a unique constraint violation error. This prevents the insertion of duplicate data and alerts the user or application to the violation.

Unique constraints play a crucial role in maintaining the integrity and consistency of data in a database. They are commonly used to enforce business rules, ensure data accuracy, and support data validation and uniqueness requirements in applications.

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