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Any column in a table can be established as the primary key, as long as it meets the following conditions:

• No two rows can have the same primary key value.

• Every row must have a primary key value. (Primary key columns may not allow NULL values.)

• Values in primary key columns should never be modified or updated.

• Primary key values should never be reused. (If a row is deleted from the table, its primary key may not be assigned to any new rows in the future.)