语句及查询结果：

--上月天数

select EXTRACT(DAY from date_trunc('month', CURRENT_DATE)- interval '0 month'- interval '1 day');

--当前时间

select now();

select current_timestamp;

--当前年月日
select current_date                    date

当前年当前月
select extract(year from now());
select extract(month from now());

得到年月日
select to_date('2012-08-20 11:12:11','yyyy-mm-dd')

得到2012-08-20                      date

select date_trunc('day', timestamp'2012-08-20 11:12:11')

得到2012-08-20 00:00:00     timestamp without time zone

加几天
select date '2001-09-28' + integer '7'

得到2001-10-05                        date

两日期间隔天数
select date '2001-10-01' - date '2001-09-28'

得到3                                           integer

两时间相减
select timestamp '2001-09-29 03:00' - timestamp '2001-09-27 12:00'

得到   1 day 15:00:00     interval

字符串先转成日期再转成字符串
select to_char(to_date('2012-08-20 11:12:11','yyyy-mm-dd'), 'yyyy-mm-dd')

得到  2012-08-20    text

函数
select age(now(), timestamp '1989-02-05');

得到24 years 4 mons 26 days 18:00:04.631114   interval

语句及查询结果：--上月天数select EXTRACT(DAY from date_trunc('month', CURRENT_DATE)- interval '0 month'- interval '1 day'); --当前时间select now();select current_timestamp;--当前年月日selec