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mysql之常见函数(几道小题目)
我就直接po代码了
#1.显示系统时间(注:日期+时间)
SELECT NOW() AS 当前时间;
#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+0.2) AS "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
last_name,
LENGTH(last_name) AS 姓名长度,
SUBSTR(last_name, 1, 1) AS "first"
FROM
employees
ORDER BY `first` ASC ;
/*
#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 ',
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:
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
last_name,
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'
WHEN 'ST_CLERK'
THEN 'E'
END AS Grade
FROM
employees
WHERE job_id = 'AD_PRES' ;
#LIMIT关键字(先感受一下,后面我再说LIMIT)
SELECT * FROM employees
ORDER BY last_name ASC
LIMIT 5;
#
SELECT * FROM employees
ORDER BY last_name ASC
LIMIT 0, 5;
#
SELECT * FROM employees
ORDER BY last_name ASC
LIMIT 5, 3;