What is a foreign key?
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The foreign key is a column that can have NULL values.
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The foreign key is a SQL locking mechanism.
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A foreign key is a key field (column) in a database table, which relates the table to another table where the key is a primary key. The primary - foreign key relations are used to cross-reference database tables.
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The foreign key is a column that should be primary key for that table.
To understand what a foreign key is, the user needs to have a basic understanding of database design.
The correct answer is:
C. A foreign key is a key field (column) in a database table, which relates the table to another table where the key is a primary key. The primary-foreign key relations are used to cross-reference database tables.
Explanation of options:
A. This option is incorrect because a foreign key cannot have NULL values. A foreign key must reference a valid primary key in another table.
B. This option is incorrect because a foreign key is not related to SQL locking mechanisms. SQL locking mechanisms are used to manage concurrent access to data.
D. This option is incorrect because a foreign key cannot be a primary key for that table. A primary key is a unique identifier for a table, while a foreign key is used to reference a primary key in another table.