SQL Administrator Question:

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A primary key is usually used as the index for a particular table — a value that the table can depend upon to be a reliable unique value in every row. When trying to pull data for a particular row, the primary key will normally be used to pull that information, usually a numeric value. For example, if you are trying to pull up data on a specific person, and that database is using their unencrypted ssn as the primary key (naughty), then that could be used in the query to identify that particular row since there could be other people present in the database with that specific name or other identifying characteristics.