Frequently Asked Questions on Unique Key
What is unique key in DBMS ?
A unique key is a constraint that ensures the values in a column or combination of columns are unique across all rows in table.
How does unique key doffer from a primary key ?
A unique key can have one NULL value but primay key cant have NULL value. Only one primary key is allowed in table but there can be more than one unique keys in a table.
Can a table have multiple unique keys?
Yes, a table can have multiple unique keys, each enforcing uniqueness within its own set of columns.
How to add unique key constraint to a column in an existing table ?
You can use the ALTER TABLE statement to add unique key constraint to a column. For example ALTER TABLR table_name, ADD CONSTRAINT contraint_name UNIQUE(column name) ; use this to add unique key.
Can a unique key constraint from a column removed after its been added ?
Yes, you can remove a unique key constraint from a column using the Alter TABLE statement, For example, ALTER TABLE table_name, DROP CONSTRAINT constraint_name; use this to delete unique key.
Unique Key in DBMS
A column or set of columns in a database system that uniquely identifies each tuple in the table is called a unique key. A unique key ensures that no two rows in the table have the same combination of values, so it enforces data integrity by preventing duplicity of the values in the table. In this article, we are going to see about the unique keys in DBMS along with their implementation in the table. Letâs start with the definition of a unique key.
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