UNIQUE Constraints

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UNIQUE Constraints

When you specify a UNIQUE constraint for a column, MySQL generates an index (UNIQUE) and blocks any attempts to enter or update data so that more than one row has the same value in that column. If you attempt to duplicate a value, you receive an error:

 Duplicate entry 'Late check-in' for key 1 

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    MySQL Database Design and Tuning
    MySQL Database Design and Tuning
    ISBN: 0672327651
    EAN: 2147483647
    Year: 2005
    Pages: 131

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