INDEXING

Indexes are something extra that you can enable on your MySQL tables to increase performance,but they do have some downsides. When you create a new index MySQL builds a separate block of information that needs to be updated every time there are changes made to the table. This means that if you are constantly updating, inserting and removing entries in your table this could have a negative impact on performance.

example 1(For Newly created table) :
CREATE TABLE employee_records ( name VARCHAR(50), employeeID INT, INDEX(employeeID));
Example 2 (For existing table) :
CREATE INDEX id_index ON employee_records2(employeeID);