oracle trunc() truncation function

Date and number can be intercepted

For example, 2010-10-15, cut to the first day of 2010, that is, 2010-01-01,
such as 20.5, cut to 20

Cut-off date

You must first understand what the cut-off date is.
Assuming date=27-10-20
trunc(date,'yyyy'), get the first day of the year

Different from to_char();

如果 2020-05-12，你想获取2020，请用`to_char(date,'yyyy');`
获取05,`to_char(date,'mm')`
获取12,`to_char(date,'dd')`

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trunc(date [, fmt ]) , return date

1. fmt omit
   output year, month and day
2. yyyy
   returns to the first day of the year等于 SYYYY YYYY YEAR SYEAR YYY YY Y
   
3. mm, the first day of the month. equalMONTH MON MM RM
   
4. ww. A date with the same day of the week as the first day of the year.
   For example, 2020-12-23, the first day of the first year is Wednesday, and 2020-12-23 happens to be Wednesday, output it;
   2020-12-22, the first day of the first year is Wednesday, output 2020-12-16 (The 16th is Wednesday) The
   output date <= the specified date.
5. DD, annual income, equal toDDD DD J 和省略fmt
6. day, the first day of the week (Sunday), equal toDAY DY D

Intercepted numbers

It's just interception, not rounding up.
trunc(n1,[,n2]) , return number

1. n2 can be omitted. Intercept the integer part like this
   

2. n2 is positive, truncated to n2 digits after the decimal point
   

3. N2 digits are negative, n2 digits before the decimal point are set to 0
   

Reference from: oracle official document
https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/TRUNC-number.html#GUID-911AE7FE-E04A-471D-8B0E-9C50EBEFE07D