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select s.id as id, s.email as email, s.password as password, s.role as role from tblStudents s
where email = "admin@admin.be"
union
select a.id as id, a.email as email, a.password as password, a.role as role from tblAdmin a
where email = "admin@admin.be"
union
select t.id as id, t.email as email, t.password as password, t.role as role from tblTeachers t
where email = "admin@admin.be"