04_单行函数

单行函数主要内容

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) 长度,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

SELECT CONCAT(last_name,' earns ',salary,' monthly but wants ',salary*3) AS "Dream Salary"
FROM employees
WHERE salary=24000;

5. 使用case-when，按照下面的条件：

SELECT last_name,job_id AS  job,
CASE job_id
WHEN 'AD_PRES' THEN 'A' 
WHEN 'ST_MAN' THEN 'B' 
WHEN 'IT_PROG' THEN 'C' 
WHEN 'SA_PRE' THEN 'D'
WHEN 'ST_CLERK' THEN 'E'
END AS Grade
FROM employees
WHERE job_id = 'AD_PRES';