Correct option is D
The
Primary Key Constraint ensures that every row in a table is unique and identifiable. It prevents duplicate rows and enforces the
uniqueness and
not null properties on the specified column(s).
Example:
Important Key Points:
1. A primary key is a combination of
Unique and
Not Null constraints.
2. Each table can have only one primary key, but it can consist of multiple columns (composite primary key).
Knowledge Booster:
·
Foreign Key: Ensures referential integrity between two tables.
·
Unique Constraint: Enforces uniqueness but allows NULL values.
·
Not Null Constraint: Ensures that a column cannot have NULL values.
·
Check Constraint: Ensures that a column satisfies a specific condition.
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