1、显示系统时间(注：日期+时间)
SELECT NOW();
2、查询员工号，姓名，工资，以及工资提高百分之20%后的结果（NEW salary）
SELECT employee_id,last_name,salary ,salary*1.2 "NEW salary"
FROM employees;
3、将员工的姓名按首字母排序，并写出姓名的长度（LENGTH）
SELECT LENGTH(last_name) ,SUBSTR(last_name,1,1) 首字符,last_name
FROM employees
ORDER BY 首字符;
4、做一个查询，产生下面的结果
# <last_name> earns <salary> monthly but wants <salary*3>
# Dream Salary
# King earns 24000 monthly but wants 72000
SELECT CONCAT(last_name,'earns',TRUNCATE(salary,0),
'monthly but wants',TRUNCATE(salary*3,0)) "DREAM SALARY"
FROM employees
WHERE salary=24000;
5、使用CASE-WHEN，按照下面的条件
#job grade
#AD_PRES A
#ST_MAN B
#IT_PROG C
#SA_REP D
#ST_CLERK E
#产生下面的结果
#Last_name Job_id Grade
#king AD_PRES A
SELECT job_id,
CASE job_id
WHEN 'AD_PRES' THEN 'A'
WHEN 'ST_MAN' THEN 'B'
WHEN 'IT_PROG' THEN 'C'
WHEN 'SA_REP' THEN 'D'
END grade
FROM employees;
