【练习】20. 日期函数

#返回从1970-01-01 00:00:00到当前毫秒值
SELECT UNIX_TIMESTAMP();
SELECT UNIX_TIMESTAMP('1980-01-01 00:01:00');
#将毫秒值转换为时间
select FROM_UNIXTIME(315529260,'%Y-%M-%D %H:%i:%s');
#返回当前日期
select CURRENT_DATE();
select CURRENT_TIME();
select CURRENT_TIMESTAMP();
#获取年月日
select date(hiredate) from emp;
#两个日期的差值(天数)
select DATEDIFF((SELECT hiredate from emp where empno = 7369),(SELECT hiredate from emp where empno = 7499));
#两个日期的差值（时分秒）
select TIMEDIFF((SELECT hiredate from emp where empno = 7369),(SELECT hiredate from emp where empno = 7499));
#日期格式化
select DATE_FORMAT(hiredate,'%d-%m-%Y') from emp
#字符串转为日期
select STR_TO_DATE(hiredate,'%Y-%m-%d') from emp;
#日期加减一定的时间
select DATE_SUB(hiredate,INTERVAL 2 day) from emp;
select DATE_add(hiredate,INTERVAL 2 day) from emp;
#在日期中获取
select EXTRACT(year from hiredate) from emp;
#获取指定月份的最后一天
select LAST_DAY(hiredate) from emp;
#某一年的第多少天的日期
select MAKEDATE(2022,99)
#根据日期获取信息
select MONTHNAME(hiredate) from emp;
select dayname(hiredate) from emp;
select DAYOFWEEK(hiredate) from emp;
select DAYOFMONTH(hiredate) from emp;
select DAYOFYEAR(hiredate) from emp;