![]() However, having several columns declared as a UNIQUE INDEX, MySQL needs to check the uniqueness constraint for each row being inserted in the column. Indexing the columns surely increases the performance if the value has to be searched in a column that is declared as a UNIQUE INDEX. Using a UNIQUE INDEX can have both a positive as well as negative impact on the performance of the database to fetch rows based on the search criteria. Contrarily, a unique index is used to ensure the uniqueness within a table.
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