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Primary Key (2 of 2) |   |
Software - Databases
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Each box in the ISBN column contains a reference number which can apply to only ONE particular book written by ONE author, published by ONE publisher. This number is unique because it can only appear once in the table; for this reason we would take this column to be the Primary Key of this table:
The primary key field must be filled for every record in a table. If several unique identifier fields exist in a table they are known as candidate keys. (No candidate keys exist in our table above).
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