A table in mysql can have multiple unique indexes. If you can determine that a data column only contains values that are different from each other, then when creating an index for this data column, you should use the keyword UNIQUE to define it as a unique index.
A table in mysql can have multiple unique indexes.
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If you can determine that a certain data column will only contain values that are different from each other, when creating an index for this data column You should use the keyword UNIQUE to define it as a unique index.
The benefits of doing this:
First, it simplifies MySQL's management of this index, and this index becomes more efficient.
Second, when a new record is inserted into the data table, MySQL will automatically check whether the value of this field of the new record has already appeared in this field of a certain record; if so, MySQL will refuse to insert that field. new records.
In other words, a unique index can ensure the uniqueness of data records. In fact, on many occasions, the purpose of creating unique indexes is not to increase access speed, but just to avoid data duplication.
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