SQL time processing (SQL server\oracle)

1、 Get the current time

#dtbegindate ：  Time in database 
#extract(MONTH FROM dtbegindate)  ： obtain dtbegindate  Months in 
#to_char (sysdate, 'yyyy-MM-dd') ：  Get the current time and convert it to fixed format character type 
#to_date (to_char (sysdate, 'yyyy-MM-dd'),'yyyy-mm-dd')：  Get the current time and convert it to time format 
#sysdate ： Get the current time 
SELECT
	dtbegindate,
	extract(MONTH FROM dtbegindate),
	to_char (sysdate, 'yyyy-MM-dd'),
	CASE
WHEN to_date (
	to_char (sysdate, 'yyyy-MM-dd'),
	'yyyy-mm-dd'
) > dtbegindate THEN
	1
ELSE
	0
END AS todatetime,
 sysdate,
 CASE
WHEN sysdate > dtbegindate THEN
	1
ELSE
	0
END AS nowtime
FROM
	bs_class

2、 Get the month of the current time

 year  select extract(year from sysdate)　from dual;

 month  select extract(month from sysdate) from dual;

 Japan  select extract(day from sysdate)　from dual;

3、oracle How to get the year in the date

select
 
to_number(to_char(t.hiredate,'yyyy'))as  Year of entry ,
 
to_number(to_char(t.hiredate,'MM'))as  Entry month ,
 
to_number(to_char(t.hiredate,'DD'))as  Days of employment 
 
 from emp t;

4、sql server 

# Get the month within the specified time 、 year 
month(c.dtDate)

year(c.dtDate)

# Change time into varchar
CONVERT(varchar(100), c.dtDate, 23)