Indexes in mysql
As a general rule of thumb, MySQL can only use one index for each table in the query. Therefore, there is no point in creating more than one index for each query. Preferably, same indexes should match as many of the queries as possible, as it will reduce the load on the database when inserting or updating data (which requires updating the indexes as well). MySQL can use indexes on columns more efficiently if they are declared as the same type and size. In this context, VARCHAR and CHAR are considered the same if they are declared as the same size. For example, VARCHAR (10) and CHAR (10) are the same size, but VARCHAR (10) and CHAR (15) are not.