Unique key
A unique key is a fundamental concept in databases, used to ensure that each record in a table is distinct and identifiable. A unique key consists of one or more columns that have a unique value for each row, which means that no two rows in the table can have the same combination of values in those columns. In relational databases, this concept is crucial for maintaining data integrity and avoiding redundancy. The unique key constraint can be applied to a column or set of columns to enforce uniqueness, which helps in ensuring that every data entry is distinguishable from others, enhancing the database accuracy and database reliability.
https://en.wikipedia.org/wiki/Unique_key
The unique key is often used in conjunction with other types of keys in databases, such as primary keys or foreign keys. While a primary key is a unique key that also enforces the non-null constraint (meaning the values in the column cannot be NULL), a unique key can allow NULL values, but still ensures that the non-NULL values are unique. In SQL queries, unique keys play an important role in maintaining the efficiency and performance of the database by reducing duplicate data entries and optimizing query results.
https://www.sqlshack.com/sql-unique-constraint-vs-primary-key-constraint/
Moreover, unique keys are essential in data modeling and in designing systems that rely on accurate identification and classification of data. For example, in an e-commerce database, a unique key could be applied to the “order ID” column to ensure each order is uniquely identified. By applying a unique key constraint, data consistency is maintained, and applications interacting with the database can trust that each record they refer to is distinct. The design and management of unique keys also assist in optimizing indexing, which further improves performance in data retrieval and search operations.
https://www.geeksforgeeks.org/unique-key-in-sql/
- Snippet from Wikipedia: Unique key
In relational database management systems, a unique key is a candidate key. All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the primary key of the relation. The remaining candidate keys are called unique keys because they can uniquely identify a record in a relation. Unique keys can consist of multiple columns. Unique keys are also called alternate keys. Unique keys are an alternative to the primary key of the relation. In SQL, the unique keys have a
UNIQUEconstraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.