1ª PREGUNTA: UNA SUBCONSULTA ES UNA CONSULTA QUE SE REALIZA DENTRO DE OTRA CONSULTA

2ª PREGUNTA: LA SUBCONSULTA SE EJECUTA UNA ÚNICA VEZ

Select first_name nombre, email, phone_number telefono from employees where job_id in ( select job_id from jobs jb where jb.job_title = "programmer")
Select first_name nombre, email, phone_number telefono from employees where job_id in select job_id from jobs where jobs.job_title = "programmer"
Select first_name nombre, email, phone_number telefono from employees where job_id in ( select job_id from jobs jb where jobs.job_title = "programmer")
Select first_name nombre, email, phone_number telefono from employees where job_id in ( select job_id from jobs jb where jb_title = "programmer")

Select count (*) from (select * from employees where employees.first_name = juan.)
Select count (*) from (select * from employees where employees.first_name = "juan")
Select count (*) from (select * from employees em where employees.first_name = "juan")
Select count (*) from (select * from employees where employees.first_name = "juan".)

Update employees set salary = salary + 1000 where department_id in (select department_id from departments where depa.department_name = "marketing")
Update employees set salary = salary + 1000 where department_id = (select department_id from departments depa where depa.department_name = "marketing")
Update employees set salary = salary + 1000 where department_id in (select department_id from departments depa where depa.department_name = "marketing")
Update employees set salary = 1000 where department_id in (select department_id from departments depa where depa.department_name = "marketing")