oracle 开发 第05章 日期函数

2016-01-08

 

一、时间值(datetime)

alter session set NLS_DATE_FORMAT ='MONTH-DD-YYYY';
alter session set NLS_DATE_FORMAT ='DD-MON-YYYY';        --设置默认时间格式
insert into customers (customer_id,first_name,last_name,dob,phone)
values (6,'Fred','Brown','05-Feb-1968','800-555-1215');

insert into customers (customer_id,first_name,last_name,dob,phone)
values (7,'Steve','Purple',DATE '1972-10-25','800-555-1215');

1.TO_CHAR(x[,format]) 　　（重点！！！）

--将时间值x转换为字符串
select customer_id,to_char(dob,'MONTH DD,YYYY') from customers;
select to_char(SYSDATE,'MONTH DD,YYYY,HH24:MI:SS') from dual;
select to_char(to_date('05-FEB-1968'),'MONTH DD, YYYY') from dual;

2.TO_DATE(x[,format])　　（重点！！！）

--将字符串转换为时间值
select to_date('04-JUL-2012'),to_date('04-JUL-12') from dual;
select to_date('July 4, 2012', 'MONTH DD, YYYY') from dual;
select to_date('7.4.12','MM.DD.YY') from dual;

insert into customers (customer_id,first_name,last_name,dob,phone)
values (6,'Fred','Brown',to_date('05-FEB-1968 19:32:36', 'DD-MON-YYYY HH24:MI:SS'),'800-555-1215');
select customer_id,to_char(dob,'DD-MON-YYYY HH24:MI:SS') from customers;

3.组合使用TO_CHAR()和TO_DATE()函数

select to_char(to_date('05-FEB-1968 19:32:36','DD-MON-YYYY HH24:MI:SS'), 'HH24:MI:SS') from dual;

select
    to_char(to_date('04-JUL-15', 'DD-MON-YY'), 'DD-MON-YYYY') as "15YY",
    to_char(to_date('04-JUL-55', 'DD-MON-YY'), 'DD-MON-YYYY') as "55YY",
    to_char(to_date('04-JUL-75', 'DD-MON-YY'), 'DD-MON-YYYY') as "75YY"
from dual;

select
    to_char(to_date('04-JUL-15', 'DD-MON-RR'), 'DD-MON-YYYY') as "15RR",
    to_char(to_date('04-JUL-55', 'DD-MON-RR'), 'DD-MON-YYYY') as "55RR",
    to_char(to_date('04-JUL-75', 'DD-MON-RR'), 'DD-MON-YYYY') as "75RR"
from dual;

4.ADD_MONTHS(x,y)

--返回x加上y个月后的日期
select add_months('01-JAN-2012',13) from dual;
select add_months('01-JAN-2012',-13) from dual;
select add_months(to_date('01-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS'),2) from dual;
select to_char(
            add_months(
                    to_date('01-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS'
                            ),2    
                      ),'DD-MON-YYYY HH24:MI:SS'
              ) from dual;

5.LAST_DAY(x)

--返回包含x的月份的最后一天
select last_day('01-JAN-2012') from dual;

6.MONTHS_BETWEEN(x,y)

--返回x和y之间有几个月
select months_between('25-MAY-2012','15-JAN-2012') from dual;
select months_between('15-JAN-2012','25-MAY-2012') from dual;

7.NEXT_DAY(x,day)

--返回从x开始，下一个day的日期
select next_day('01-JAN-2012','SATUERDAY') from dual;

8.ROUND(x[,unit])

--对x取整，默认取整为最近的一天
select round(to_date('25-OCT-2012'),'YYYY') from dual;
select round(to_date('25-MAY-2012'),'MM') from dual;
select to_char(
            round(
                to_date('25-MAY-2012 19:45:26','DD-MON-YYYY HH24:MI:SS'
                       ),'HH24'
                ),'DD-MON-YYYY HH24:MI:SS'
              ) 
from dual;

9.SYSDATE

--返回数据库服务器所在操作系统当前日期
select sysdate from dual;

10.TRUNC(x[,unit])

--对x截断，默认截断为当天开始时间
select trunc(to_date('25-MAY-2012'),'YYYY') from dual;
select trunc(to_date('25-MAY-2012'),'MM') from dual;
select to_char(
                trunc(
                    to_date(
                            '25-MAY-2012 19:45:26','DD-MON-YYYY HH24:MI:SS'
                           ),'HH24'
                    ),'DD-MON-YYYY HH24:MI:SS'
              )
from dual;

二、时区(timezone)
+00:00
GMT(Green Mean Time) 格林威治时间(旧称)
UTC(Coordinated Universal Time)协调世界时间(新称)
-08:00
PST(Pacific Standard Time)太平洋标准时间
-05:00
EST(Eastern Standard Time)美国东部标准时间

alter database set time_zone = offset |region    --修改数据库时区
alter database set time_zone = '-8:00'
alter database set time_zone = 'PST'

alter session set time_zone = 'EST';            --修改会话时区

select dbtimezone from dual;        --查看数据库时区
select sessiontimezone from dual;    --查看会话时区
select current_date from dual;        --查看会话时区的当前日期
select tz_offset('PST') from dual;    --获取时区的时差

conn system;
select tzname,tzabbrev
from v$timezone_names
where rownum <= 5
order by tzabbrev;                    --获取时区名

select to_char(
               new_time(
                           to_date(
                                   '25-MAY-2012 19:45','DD-MON-YYYY HH24:MI'
                                   ),'PST','EST'
                          ),'DD-MON-YYYY HH24:MI'
              )
from dual;                            --将时间值从一个时区转换到另一个时区

三、时间戳(timestamp)
1.时间戳类型
--时间戳可以存储秒的小数位、时区
1.1 timstamp类型

create table purchases_with_timestamp (
    product_id integer references products(product_id),
    customer_id integer references customers(customer_id),
    made_on timestamp(4));

insert into purchases_with_timestamp (product_id,customer_id,made_on) 
values (1,1,timestamp '2005-05-13 07:15:31.1234');
select * from purchases_with_timestamp;

1.2 timstamp with time zone类型

create table purchases_timestamp_with_tz (
    product_id integer references products(product_id),
    customer_id integer references customers(customer_id),
    made_on timestamp(4) with time zone);

insert into purchases_timestamp_with_tz (product_id,customer_id,made_on) 
values (1,1,timestamp '2005-05-13 07:15:31.1234 -07:00');
insert into purchases_timestamp_with_tz (product_id,customer_id,made_on) 
values (1,2,timestamp '2005-05-13 07:15:31.1234 PST');
select * from purchases_timestamp_with_tz;

1.3 timstamp with local time zone类型

create table purchases_with_local_tz (
    product_id integer references products(product_id),
    customer_id integer references customers(customer_id),
    made_on timestamp(4) with local time zone);

insert into purchases_with_local_tz (product_id,customer_id,made_on) 
values (1,1,timestamp '2005-05-13 07:15:30 EST');

select * from purchases_with_local_tz;

2.时间戳函数
2.1 CURRENT_TIMESTAMP、LOCAL TIMESTAMP、SYSTIMESTAMP

select current_timestamp,localtimestamp,systimestamp from dual;
alter session set time_zone = 'EST';
select current_timestamp,localtimestamp,systimestamp from dual;
alter session set time_zone = 'PST';

2.2 EXTRACT({YEAR|MONTH|DAY|HOUR|MINUTE|SECOND}|
{TIMEZONE_HOUR|TIMEZONE_MINUTE}|{TIMEZONE_REGION|TIMEZONE_ABBR} FROM x)

--从x中提取并返回年、月、日、时、分、秒、时区，x可以是DATE或TIMESTAMP类型
select
    extract(year from to_date('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as YEAR,
    extract(month from to_date('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as MONTH,
    extract(day from to_date('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as DAY
from dual;

select
    extract(hour from to_timestamp('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as HOUR,
    extract(minute from to_timestamp('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as MINUTE,
    extract(second from to_timestamp('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS')) as SECOND
from dual;

select
    extract(timezone_hour from to_timestamp_tz('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS TZH:TZM')) as TZH,
    extract(timezone_minute from to_timestamp_tz('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS TZH:TZM')) as TZM,
    extract(timezone_region from to_timestamp_tz('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS TZR')) as TZR,
    extract(timezone_abbr from to_timestamp_tz('05-JAN-2012 19:15:26','DD-MON-YYYY HH24:MI:SS TZR')) as TZA
from dual;

2.3 FROM_TZ(x,time_zone)

--将timestamp类型的x转换为time_zone指定的时区，并返回timestamp with timezone类型的值
select from_tz(timestamp '2012-05-13 07:15:31.1234', '-7:00') from dual;

2.4 SYS_EXTRACT_UTC(x)

--将timestamp with timezone类型的x转换为包含UTC时区日期和时间的timestamp类型
select sys_extract_utc(timestamp '2012-11-17 19:15:26 PST') from dual;
select sys_extract_utc(timestamp '2012-05-17 19:15:26 PST') from dual;

2.5 TO_TIMESTAMP(x[,format])

--将字符串x转换为timestamp类型,x可以为CHAR/VARCHAR2/NCHAR/NVARCHAR2类型
select to_timestamp('2012-05-13 07:15:31.1234','YYYY-MM-DD HH24:MI:SS.FF') from dual;

 2.6 TO_TIMESTAMP_TZ(x[,format])

--将字符串x转换为timestamp with timezone类型
select to_timestamp_tz('2012-05-13 07:15:31.1234 PST','YYYY-MM-DD HH24:MI:SS.FF TZR') from dual;
select to_timestamp_tz('2012-05-13 07:15:31.1234 -7:00','YYYY-MM-DD HH24:MI:SS.FF TZM') from dual;

2.7 CAST(x as type)

--将字符串x转换为timestamp with local time stamp类型
select cast('13-JUN-12' as timestamp with local time zone) from dual;
select cast(
            to_timestamp_tz(
                            '2012-05-13 07:15:31.1234 PST','YYYY-MM-DD HH24:MI:SS.FF TZR'
                            ) as timestamp with local time zone
            ) 
from dual;

select cast(
            to_timestamp_tz(
                            '2012-05-13 07:15:31.1234 EST','YYYY-MM-DD HH24:MI:SS.FF TZR'
                            ) as timestamp with local time zone
            ) 
from dual;

四、时间间隔(time interval)
1.时间间隔类型
1.1 interval year to month类型

--interverl '[+|-][y][-m] [year[(years_precision)]] [to month]'
create table coupons (
    coupon_id integer constraint coupons_pk primary key,
    name varchar2(30) not null,
    duration interval year(3) to month);
insert into coupons (coupon_id,name,duration) values (1,'$1 off Z Files',interval '1' year);
insert into coupons (coupon_id,name,duration) values (2,'$2 off Pop 3',interval '11' month);
insert into coupons (coupon_id,name,duration) values (3,'$3 off Modern Science',interval '14' month);
insert into coupons (coupon_id,name,duration) values (4,'$2 off Tank War',interval '1-3' year to month);
insert into coupons (coupon_id,name,duration) values (5,'$1 off Chemistry',interval '0-5' year to month);
insert into coupons (coupon_id,name,duration) values (6,'$2 off Creative Yell',interval '123' year(3));

1.2 interval day to second类型

--interval '[+|-][d] [h[:m[:s]]]' [day[(days_precision)]] to hour|minute|second[(second_precision)]
create table promotions (
    promotion_id integer constraint promotions_pk primary key,
    name varchar2(30) not null,
    duration interval day(3) to second(4));
insert into promotions (promotion_id,name,duration) values (1,'10% off Z Files',interval '3' day);
insert into promotions (promotion_id,name,duration) values (2,'20% off Pop 3',interval '2' hour);
insert into promotions (promotion_id,name,duration) values (3,'30% off Modern Science',interval '25' minute);
insert into promotions (promotion_id,name,duration) values (4,'20% off Tank War',interval '45' second);
insert into promotions (promotion_id,name,duration) values (5,'10% off Chemistry',interval '3 2:25' day to minute);
insert into promotions (promotion_id,name,duration) values (6,'20% off Creative Yell',interval '3 2:25:45' day to second);
insert into promotions (promotion_id,name,duration) values (7,'15% off My Front Line',interval '123 2:25:45.12' day(3) to second(2));

2.时间间隔函数
2.1 NUMTODSINTERVAL(x,interval_unit)

--将x转换为interval day to second类型
select
    numtodsinterval(1.5,'day'),
    numtodsinterval(3.25,'hour'),
    numtodsinterval(5,'minute'),
    numtodsinterval(10.123456789,'second')
from dual;

2.2 numtoyminterval(x,interval_unit)

--将x转换为interval year to month类型
select
    numtoyminterval(1.5,'year'),
    numtoyminterval(3.25,'month')
from dual;

 

【参考资料】

[1] Jason Price.精通Oracle Database 12c SQL&PLSQL编程(第3版).[M].北京：清华大学出版社，2014