Database design: 4 types of users but have different functionality , separate or one table? I have 4 types of users:

Admins , normal user , company , service provider

Admins and normal user share some attributes (id .first name ,last name ,phone ,mail) company and service provider share some attributes too (id .company name ,phone ,fax ,mail ).

They interact too with other entities in application to access some feature like post job or event or apply for it

Is it better to put them all in one user table like tbl_users or is it better to create separate table to every one ? or add to two tables one for (Admins and normal user) and other for ( company and service provider)
A simple design you can go for is to choose three tables

Table MasterUser

UserId - PK - Identity(auto increment) 
phone
mail


Table AdminNormalUser

UserId -- Pk of this table and UserId of `MasterUser`
FirstName
LastName


Table CompanyPorviderUser

UserId -- Pk of this table and UserId of `MasterUser`
CompanyName
Fax 


This design will give you a unique Id to each user, no matter a Admin, Normal, Company or provider user, which is a requirement for application that will use these tables, And it will get rid of columns with NULL values.