Posted by / 18-Aug-2015 07:28

If there had been any rows in second table that did not have matches in first table, those rows also would have been listed.

Tables or result sets sometimes contain duplicate records.

This chapter will describe how to prevent duplicate records occurring in a table and how to remove already existing duplicate records.You can use a PRIMARY KEY or UNIQUE Index on a table with appropriate fields to stop duplicate records.Let's take one example: The following table contains no such index or primary key, so it would allow duplicate records for first_name and last_name.To prevent multiple records with the same first and last name values from being created in this table, add a PRIMARY KEY to its definition.Sometimes, it is allowed but sometimes it is required to stop duplicate records.


Sometimes, it is required to identify duplicate records and remove them from the table.

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