What exactly is inside a database index?
So, now you know that a database index is created on a column in a table, and that the
index stores the values in that specific column. But, it is important to understand that
a database index does not store the values in the other columns of the same table. For
example, if we create an index on the Employee_Name column, this means that the
Employee_Age and Employee_Address column values are not also stored in the
index. If we did just store all the other columns in the index, then it would be just like
creating another copy of the entire table – which would take up way too much space
and would be very inefficient.