The Modern SQL Twitter account (by Markus Winand) published a hint about how to extract a date part in SQL:
 
 
 
 
 
 
 
 
 
 

The right way to get a part of a date/time is:

EXTRACT(YEAR FROM CURRENT_DATE) = 2015http://t.co/UNLyUoQdVb

Retweet to spread the word!

— Modern SQL (@ModernSQL) February 24, 2015

Is it true? Yes it is, in the SQL standard and in a variety of standards-compliant databases. But let’s check what jOOQ does when you run the following program on all 18 currently supported RDBMS:

import static org.jooq.impl.DSL.currentDate;
import static org.jooq.impl.DSL.extract;
import static org.jooq.impl.DSL.using;

import java.util.stream.Stream;

import org.jooq.DatePart;
import org.jooq.SQLDialect;

public class Extract {
 public static void main(String[] args) {
 // Get all distinct SQLDialect families
 Stream
 .of(SQLDialect.values())
 .map(SQLDialect::family)
 .distinct()
 .forEach(family -> {
 System.out.println();
 System.out.println(family);

 // Get all supported date parts
 Stream
 .of(DatePart.values())

 // For each family / part, get the
 // EXTRACT() function
 .map(part -> extract(currentDate(), part))
 .forEach(expr -> {
 System.out.println(
 using(family).render(expr)
 );
 });
 });
 }
}

The output is:

Open Source databases

DEFAULT
extract(year from current_date())
extract(month from current_date())
extract(day from current_date())
extract(hour from current_date())
extract(minute from current_date())
extract(second from current_date())

CUBRID
extract(year from current_date())
extract(month from current_date())
extract(day from current_date())
extract(hour from current_date())
extract(minute from current_date())
extract(second from current_date())

DERBY
year(current_date)
month(current_date)
day(current_date)
hour(current_date)
minute(current_date)
second(current_date)

FIREBIRD
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from current_date)
extract(minute from current_date)
extract(second from current_date)

H2
extract(year from current_date())
extract(month from current_date())
extract(day from current_date())
extract(hour from current_date())
extract(minute from current_date())
extract(second from current_date())

HSQLDB
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from current_date)
extract(minute from current_date)
extract(second from current_date)

MARIADB
extract(year from current_date())
extract(month from current_date())
extract(day from current_date())
extract(hour from current_date())
extract(minute from current_date())
extract(second from current_date())

MYSQL
extract(year from current_date())
extract(month from current_date())
extract(day from current_date())
extract(hour from current_date())
extract(minute from current_date())
extract(second from current_date())

POSTGRES
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from current_date)
extract(minute from current_date)
extract(second from current_date)

SQLITE
strftime('%Y', current_date)
strftime('%m', current_date)
strftime('%d', current_date)
strftime('%H', current_date)
strftime('%M', current_date)
strftime('%S', current_date)

Commercial databases

ACCESS
datepart('yyyy', date())
datepart('m', date())
datepart('d', date())
datepart('h', date())
datepart('n', date())
datepart('s', date())

ASE
datepart(yy, current_date())
datepart(mm, current_date())
datepart(dd, current_date())
datepart(hh, current_date())
datepart(mi, current_date())
datepart(ss, current_date())

DB2
year(current_date)
month(current_date)
day(current_date)
hour(current_date)
minute(current_date)
second(current_date)

HANA
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from current_date)
extract(minute from current_date)
extract(second from current_date)

INFORMIX
year(current year to day)
month(current year to day)
day(current year to day)
current year to day::datetime hour to hour::char(2)::int
current year to day::datetime minute to minute::char(2)::int
current year to day::datetime second to second::char(2)::int

INGRES
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from current_date)
extract(minute from current_date)
extract(second from current_date)

ORACLE (in jOOQ 3.5)
to_char(trunc(sysdate), 'YYYY')
to_char(trunc(sysdate), 'MM')
to_char(trunc(sysdate), 'DD')
to_char(trunc(sysdate), 'HH24')
to_char(trunc(sysdate), 'MI')
to_char(trunc(sysdate), 'SS')

ORACLE (in jOOQ 3.6)
extract(year from current_date)
extract(month from current_date)
extract(day from current_date)
extract(hour from cast(current_date as timestamp))
extract(minute from cast(current_date as timestamp))
extract(second from cast(current_date as timestamp))

SQLSERVER
datepart(yy, convert(date, current_timestamp))
datepart(mm, convert(date, current_timestamp))
datepart(dd, convert(date, current_timestamp))
datepart(hh, convert(date, current_timestamp))
datepart(mi, convert(date, current_timestamp))
datepart(ss, convert(date, current_timestamp))

SYBASE
datepart(yy, current date)
datepart(mm, current date)
datepart(dd, current date)
datepart(hh, current date)
datepart(mi, current date)
datepart(ss, current date)

Yes. The standard… If only it were implemented thoroughly…