#案例：返回location_id是1400或1700的部门中的所有员工

SELECT  last_name
FROM employees 
WHERE department_id IN(

    SELECT DISTINCT department_id
    FROM departments
    WHERE location_id IN (1400,1700)
);

#案例：返回其他工种中比job_id为'IT_PROG'部门任一工资低的员工的员工号、姓名、job_id和salary

SELECT DISTINCT employee_id,last_name,job_id,salary
FROM employees
WHERE salary'IT_PROG' ;

或者

SELECT DISTINCT employee_id,last_name,job_id,salary
FROM employees
WHERE salary<(
    SELECT DISTINCT MAX(salary)
    FROM employees
    WHERE job_id='IT_PROG'
) AND job_id <>'IT_PROG' ;

#案例：返回其他工种中比job_id为'IT_PROG'部门所有工资低的员工的员工号、姓名、job_id和salary

SELECT DISTINCT employee_id,last_name,job_id,salary
FROM employees
WHERE salary'IT_PROG' ;

或者

SELECT DISTINCT employee_id,last_name,job_id,salary
FROM employees
WHERE salary<(
    SELECT DISTINCT MIN(salary)
    FROM employees
    WHERE job_id='IT_PROG'
) AND job_id <>'IT_PROG' ;