What is a KEY or INDEX in MySQL and How Does it Improve Data Retrieval?

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:

• Not a Primary Key: The KEY constraint does not enforce uniqueness on the ug_main_grp_id column.
• Not a Foreign Key: The KEY constraint does not reference another table.
• Index with No Special Features: This KEY index does not have any additional indexing options specified, such as UNIQUE, FULLTEXT, or SPATIAL.

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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