1. 下面的语句是否可以执行成功

      1. select last_name , job_id , salary as sal from employees;

    2. 下面的语句是否可以执行成功

      select * from employees;

    3. 找出下面语句中的错误

      SELECT employee_id , last_name,salary * 12 AS "ANNUAL  SALARY" FROM employees;

    4. 显示表departments的结构，并查询其中的全部数据

      desc departments
select * from departments;

    5. 显示出表employees中的全部job_id（不能重复）

      select distinct job_id from employees;

    6. 显示出表employees的全部列，各个列之间用逗号连接，列头显示成OUT_PUT

      select concat(first_name,',',last_name,',',email,',',ifnull(commission_pct,0)) as out_put from employees