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I have one UNIQUE field in my table, and I need to search over it quickly. Do I need to index it?
Do searches over unique fields and indexed fields vary in speed or resource usage?
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MySQL allows another constraint called the UNIQUE INDEX to enforce the uniqueness of values in one or more columns. We can create more than one UNIQUE index in a single table, which is not possible with the primary key constraint.
Benefits of a Unique IndexProvided that the data in each column is unique, you can create both a unique clustered index and multiple unique nonclustered indexes on the same table. Unique indexes ensure the data integrity of the defined columns.
No, you dont have to index it again. When you specify UNIQUE KEY, the column is indexed. So it has no difference in performance with other indexed column (e.g. PRIMARY KEY) of same type.
However if the type is different, there will be little performance difference.
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Every UNIQUE field is by definition indexed with a UNIQUE INDEX - this also happens to be the fastest searchable access path.
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