Which is/are correct statements about primary key of a table?Primary keys can contain NULL valuesPrimary keys cannot contain NULL values.A table can have only one primary key with single or multiple fieldsA table can have multiple primary keys with single or multiple fields
Question
Which is/are correct statements about primary key of a table?Primary keys can contain NULL valuesPrimary keys cannot contain NULL values.A table can have only one primary key with single or multiple fieldsA table can have multiple primary keys with single or multiple fields
Solution
The correct statements about the primary key of a table are:
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Primary keys cannot contain NULL values. This is because the primary key's main function is to uniquely identify each record in a database table. A NULL value is considered as unknown or not applicable, so it cannot be used to uniquely identify a record.
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A table can have only one primary key with single or multiple fields. This is because the primary key is the main way to identify a record. If a table had multiple primary keys, it could lead to confusion and data integrity issues. However, a primary key can consist of one or more fields, known as a composite primary key.
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