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hari
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Asked: 2021-09-14T04:08:59+00:00 In:

Key Differences Between Primary key and Unique key in mysql

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Key Differences Between Primary key and Unique key in mysql

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    1. Primary Key:

      • There can only be one primary key in a table
      • In some DBMS it cannot be NULL – e.g. MySQL adds NOT NULL
      • Primary Key is a unique key identifier of the record

      Unique Key:

      • Can be more than one unique key in one table
      • Unique key can have NULL values
      • It can be a candidate key
      • Unique key can be NULL ; multiple rows can have NULL values and therefore may not be considered “unique”
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