Try doing as follows:
Start from a higher-level description of the database! As you have employees, and employees can be "ce" employees and "sn" employees (whatever those are). In oo(object-oriented terms), there is a class named as "employee", with two sub-classes named as "ce employee" and "sn employee". Now, you can translate this higher-level description to three tables as follows: employees, employees_ce and employees_sn:
employees_ce(id, ce-specific stuff)
employees_sn(id, sn-specific stuff)
Since all employees are employees, every employee must have a row in the employees table. "ce" employees will also have a row in the employees_ce table, and "sn" employees will also have a row in the employees_sn table. Here, employees_ce.id is the foreign key to employees.id, just as employees_sn.id is.
Refer to the employees table: you can refer to an employee of any kind like (ce or sn).