Obrigado por atualizar a consulta; agora podemos ver que a condição WHERE é aplicada apenas ao último Consulta UNION. Você precisa ou adicione essa cláusula WHERE a cada consulta ou envolva-a como uma subseleção e aplique a cláusula WHERE a isso.
select s.id as id, s.email as email, s.password as password, s.role as role from tblStudents s
where email = "[email protected]"
union
select a.id as id, a.email as email, a.password as password, a.role as role from tblAdmin a
where email = "[email protected]"
union
select t.id as id, t.email as email, t.password as password, t.role as role from tblTeachers t
where email = "[email protected]"
ou
SELECT * FROM (
select s.id as id, s.email as email, s.password as password, s.role as role from tblStudents s
union
select a.id as id, a.email as email, a.password as password, a.role as role from tblAdmin a
union
select t.id as id, t.email as email, t.password as password, t.role as role from tblTeachers t
) foo where email = "[email protected]"
