Oracle TRUNC function processing date format

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From the official blog of Sunda Technology
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Another explanation , After interception, the result is still date data type

select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’) from dual; -- Display current time
2011-12-29 16:24:34
select trunc(sysdate,‘year’) from dual; -- Cut to year （ The first day of the year ）
2011-1-1
select trunc(sysdate,‘q’) from dual; -- Intercept to quarter （ The first day of the quarter ）
2011-10-1
select trunc(sysdate,‘month’) from dual; -- Intercept to month （ The first day of the month ）
2011-12-1
select trunc(sysdate,’’) from dual;
empty
select to_char(trunc(sysdate),‘yyyymmdd hh24:mi:ss’) from dual; -- The default interception date is （ Zero minute and zero second of the day ）
20111229 00:00:00
trunc(sysdate) This is the intercept date section , When you need to use dates for grouping , You can use this function , As shown below edit by sand

select trunc(sysdate-1,‘w’) from dual; – The Thursday closest to the current time , If the current day is Thursday, return to the current day , Otherwise, return to last Thursday
2011-12-22
select trunc(sysdate,‘ww’) from dual; -- Intercepted last weekend （ Last Saturday ）
2011-12-24
select trunc(sysdate,‘day’) from dual; -- Intercept to week （ First day of the week , Last Sunday ）
2011-12-25
select trunc(sysdate,‘iw’) from dual; -- This week 2 God , This Monday
2011-12-26
select to_char(trunc(sysdate,‘dd’),‘yyyymmdd hh24:mi:ss’) from dual;– Intercept to day （ Zero minute and zero second of the day ）
20111229 00:00:00
select trunc(sysdate,‘hh24’) from dual; -- Intercept to hours （ Current hour , Zero minute zero second ）
2011-12-29 16:00:00
select trunc(sysdate,‘mi’) from dual; -- Intercept points （ The current points , Zero seconds ）
2011-12-29 16:24:00
select trunc(sysdate,‘ss’) from dual ;– Report errors , There is no format accurate to seconds

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From the official blog of Sunda Technology
http://www.cnsendblog.com/index.php/?p=2204