code for approve, reject and pending button

So you need to maintain role type for each user type.

You can define a Role table with RoleId and RoleName. Here you define the name such as "Requestor", "Manager" and "Security".

The id can be mapped by directly having one new column Role in Users table, which will store the RoleId from Role table or having another table UserRoles with UserId and RoleId columns.