An index may be created on

Explanation

An index can be created on any of the following:• Primary key: A primary key uniquely identifies a row in a table. Creating an index on the primary key allows for fast retrieval of specific rows.• Secondary key: A secondary key is a column, or set of columns, that uniquely identifies rows within a table, but is not the primary key. Indexes on secondary keys can also speed up retrieval of data based on those columns.• Foreign key: A foreign key is a column, or set of columns, in one table that references the primary key of another table. Creating an index on a foreign key can improve the performance of joins between tables.In essence, creating an index on any column or set of columns that you frequently query by can improve the performance of your database queries