SQL Indexes

• You can create SQL indexes from single or multiple columns.
• A SQL index is like the index of a book. It speeds up the retrieval of a record. The relational database management system (RDBMS) can retrieve a record with the index key instead of having to perform a table scan.
• MySQL automatically creates indexes for primary and foreign keys significantly speeding up join performance.
• You should only create indexes on columns used in a join or search because the RDMS must update an index every time you execute an INSERT, UPDATE, or DELETE.