suresh The Difference Between Primary Key and Unique Key Constraint in a Database
When it comes to database design, understanding the difference between a primary key and a unique key constraint is essential. Both primary keys and unique keys are used to enforce uniqueness of data values in a table, but they serve different purposes.
Primary Key: The primary key is a column or a set of columns that uniquely identifies each row in a table. It ensures that the values in the key columns are unique and not null. A table can have only one primary key, and it is used to enforce entity integrity.
Unique Key Constraint: On the other hand, a unique key constraint also enforces uniqueness, but it allows one null value. Multiple unique key constraints can be defined in a table, and they are used to prevent duplicate values in a column or a combination of columns.
Therefore, the main difference between a primary key and a unique key constraint is that a primary key does not allow null values and is used to uniquely identify each row in a table, while a unique key constraint allows one null value and is used to enforce uniqueness within a column or set of columns.
Understanding the distinctions between these two key types is fundamental for creating a well-structured and efficient database schema.
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