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Understanding the KEY Keyword in MySQL
In the provided MySQL table definition, a KEY constraint has been defined on the ug_main_grp_id column. The KEY keyword is often used interchangeably with INDEX in MySQL.
What is a KEY or INDEX?
A KEY or INDEX in MySQL is a special data structure that speeds up data retrieval by providing a quicker search mechanism than a sequential scan of the entire table. It creates a mapping between the indexed column(s) and the row's physical location on disk.
Special Characteristics of the KEY Index
The KEY index in the example you provided has a few specific characteristics:
Therefore, the KEY index in this case is a regular index created for optimizing data retrieval performance. It can be used to quickly find rows based on the values in the ug_main_grp_id column.
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