Question

You cannot enter ________ or _________ values in a Primary key field.
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Answer 1

You cannot enter DUPLICATE or NULL values in a Primary key field.

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Explanation:

• The primary key field is a unique field in a table that helps in identifying the record in a database table.

• Every table should contain one primary key and the values in those fields should be not-null and unique.

• If there are more than one unique representation fields, such fields are known as composite key fields (Other than the one that is chosen as a primary key field).

• Altering a primary key: ALTER TABLE TABLE_NAME ADD PRIMARY KEY (COLUMN_NAME);

• Here, the column name should be the primary key field that holds the not-null and unique values. 'Id' can be the best example for the primary-key field, as no id number would be same or null.

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