Date/Time Values

Table of contents:

Date Time Values

PostgreSQL supports four basic temporal data types plus a couple of extensions that deal with time zone issues.

The DATE type is used to store dates. A DATE value stores a century, year, month, and day.

The TIME data type is used to store a time-of-day value. A TIME value stores hours, minutes, seconds, and microseconds. It is important to note that a TIME value does not contain a time zoneif you want to include a time zone, you should use the type TIME WITH TIME ZONE. TIMETZ is a synonym for TIME WITH TIME ZONE.

The TIMESTAMP data type combines a DATE and a TIME, storing a century, year, month, day, hour, minutes, seconds, and microseconds. Unlike the TIME data type, a TIMESTAMP does include a time zone. If, for some reason, you want a date/time value that does not include a time zone, you can use the type TIMESTAMP WITHOUT TIME ZONE.

The last temporal data type is the INTERVAL. An INTERVAL represents a span of time. I find that the easiest way to think about INTERVAL values is to remember that an INTERVAL stores some (possibly large) number of seconds, but you can group the seconds into larger units for convenience. For example, the CAST( '1 week' AS INTERVAL ) is equal to CAST( '604800 seconds' AS INTERVAL ), which is equal to CAST( '7 days' AS INTERVAL ) you can use whichever format you find easiest to work with.

Table 2.9 lists the size and range for each of the temporal data types.

Table 2.9. Temporal Data Type Sizes and Ranges

Data Type

Size (in bytes)

Range

DATE

4

-01-MAR-4801 BC 31-DEC-32767

TIME [ WITHOUT TIME ZONE ]

4

-00:00:00.00 23:59:59.99

TIME WITH TIME ZONE

12

-00:00:00.00+12 23:59:59.00-12

TIMESTAMP [ WITH TIME ZONE ]

8

-24-NOV-4714 BC 31-DEC- 5874897

TIMESTAMP WITHOUT TIME ZONE

8

-24-NOV-4714 BC 31-DEC- 5874897

INTERVAL

12

--178000000 YEARS +178000000 YEARS

The data types that contain a time value (TIME, TIME WITH TIME ZONE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, and INTERVAL) have microsecond precision. The DATE data type has a precision of one day.

Syntax for Literal Values

I covered date literal syntax pretty thoroughly in Chapter 1; see the section titled "Working with Date Values."

You may recall from Chapter 1 that date values can be entered in many formats, and you have to tell PostgreSQL how to interpret ambiguous values. Fortunately, the syntax for TIME, TIMESTAMP, and INTERVAL values is much more straightforward.

A TIME value stores hours, minutes, seconds, and microseconds. The syntax for a TIME literal is

hh:mm[:ss[.µ ]][AM|PM]µ

where hh specifies the hour, mm specifies the number of minutes past the hour, ss specifies the number of seconds, and µ specifies the number of microseconds. If you include an AM or PM indicator, the hh component must be less than or equal to 12; otherwise, the hour can range from 0 to 24.

Entering a TIME WITH TIME ZONE value is a bit more complex. A TIME WITH TIME ZONE value is a TIME value, plus a time zone. The time zone component can be specified in two ways. First, you can include an offset (in minutes and hours) from UTC:

hh:mm[:ss[.µ ]][AM|PM][{+|-}HH[:MM]]

where HH is the number of hours and MM is the number of minutes distant from UTC. Negative values are considered to be west of the prime meridian, and positive values are east of the prime meridian.

You can also use a standard time zone abbreviation (such as UTC, PDT, or EST) to specify the time zone:

hh:mm[:ss[.µ ]][AM|PM][ZZZ]

Table 2.10 shows all the time zone abbreviations accepted by PostgreSQL version 8.0.

Table 2.10. PostgreSQL Time Zone Names

Names

Offset

Description

FJST

-13:00

Fiji Summer Time

FJT

-12:00

Fiji Time

IDLW

-12:00

International Date Line, West

BST

-11:00

Bering Summer Time

NT

-11:00

Nome Time

NUT

-11:00

Niue Time

AHST

-10:00

Alaska-Hawaii Std Time

CAT

-10:00

Central Alaska Time

HST

-10:00

Hawaii Std Time

THAT

-10:00

Tahiti Time

TKT

-10:00

Tokelau Time

MART

-09:30

Marquesas Time

AKST

-09:00

Alaska Standard Time

GAMT

-09:00

Gambier Time

HDT

-09:00

Hawaii/Alaska Daylight Time

YST

-09:00

Yukon Standard Time

AKDT

-08:00

Alaska Daylight Time

PST

-08:00

Pacific Standard Time

YDT

-08:00

Yukon Daylight Time

MST

-07:00

Mountain Standard Time

PDT

-07:00

Pacific Daylight Time

CST

-06:00

Central Standard Time

EAST

-06:00

Easter Island Time

GALT

-06:00

Galapagos Time

MDT

-06:00

Mountain Daylight Time

ZP6

-06:00

UTC +6 hours

ACT

-05:00

Atlantic/Porto Acre Time

CDT

-05:00

Central Daylight Time

COT

-05:00

Columbia Time

EASST

-05:00

Easter Island Summer Time

ECT

-05:00

Ecuador Time

EST

-05:00

Eastern Standard Time

PET

-05:00

Peru Time

ZP5

-05:00

UTC +5 hours

ACST

-04:00

Atlantic/Porto Acre Summer Time

AMT

-04:00

Amazon Time (Porto Velho)

AST

-04:00

Atlantic Std Time (Canada)

BOT

-04:00

Bolivia Time

CLT

-04:00

Chile Time

ECT

-04:00

Eastern Caribbean Time

EDT

-04:00

Eastern Daylight Time

GYT

-04:00

Guyana Time

PYT

-04:00

Paraguay Time

VET

-04:00

Venezuela Time

ZP4

-04:00

UTC +4 hours

NFT

-03:30

Newfoundland Standard Time

NST

-03:30

Newfoundland Standard Time

ADT

-03:00

Atlantic Daylight Time

AMST

-03:00

Amazon Summer Time (Porto Velho)

ART

-03:00

Argentina Time

AWT

-03:00

Brazil Time

BRT

-03:00

Brasilia Time

BST

-03:00

Brazil Standard Time

CLST

-03:00

Chile Summer Time

FKST

-03:00

Falkland Islands Summer Time

GFT

-03:00

French Guiana Time

PYST

-03:00

Paraguay Summer Time

UYT

-03:00

Uruguay Time

WGT

-03:00

West Greenland Time

NDT

-02:30

Newfoundland Daylight Time

BRST

-02:00

Brasilia Summer Time

FKT

-02:00

Falkland Islands Time

FNT

-02:00

Fernando de Noronha Time

PMDT

-02:00

Pierre & Miquelon Daylight Time

UYST

-02:00

Uruguay Summer Time

WGST

-02:00

West Greenland Summer Time

AZOT

-01:00

Azores Time

EGT

-01:00

East Greenland Time

FNST

-01:00

Fernando de Noronha Summer Time

SET

-01:00

Seychelles Time

WAT

-01:00

West Africa Time

AZOST

+00:00

Azores Summer Time

EGST

+00:00

East Greenland Summer Time

GMT

+00:00

Greenwich Mean Time

UTC

+00:00

Universal Coordinated Time

UT

+00:00

Universal Time

WET

+00:00

Western Europe

ZULU

+00:00

Universal Time

Z

+00:00

ISO-8601 Universal Time

BST

+01:00

British Summer Time

CET

+01:00

Central European Time

DNT

+01:00

Dansk Normal Time

FST

+01:00

French Summer Time

MET

+01:00

Middle Europe Time

MEWT

+01:00

Middle Europe Winter Time

MEZ

+01:00

Middle Europe Zone

NOR

+01:00

Norway Standard Time

SWT

+01:00

Swedish Winter Time

WEST

+01:00

Western Europe Summer Time

WEtdST

+01:00

Western Europe Daylight Savings Time

BDST

+02:00

British Double Summer Time

CEST

+02:00

Central European Dayl.Time

CETDST

+02:00

Central European Dayl.Time

EET

+02:00

Eastern Europe, USSR Zone 1

FWT

+02:00

French Winter Time

IST

+02:00

Israel Time

MEST

+02:00

Middle Europe Summer Time

MEtdST

+02:00

Middle Europe Daylight Time

SST

+02:00

Swedish Summer Time

BT

+03:00

Baghdad Time

EAT

+03:00

East Africa Time

EAT

+03:00

Indian Antananarivo Time

EEST

+03:00

Eastern Europe Summer Time

EEtdST

+03:00

Eastern Europe Daylight Time

HMT

+03:00

Hellas Mediterranean Time

MSK

+03:00

Moscow Time

IRT

+03:30

Iran Time

IT

+03:30

Iran Time

AMT

+04:00

Armenia Time (Yerevan)

AZT

+04:00

Azerbaijan Time

EAST

+04:00

Indian Antananarivo Savings Time

GET

+04:00

Georgia Time

MSD

+04:00

Moscow Summer Time

MUT

+04:00

Mauritius Island Time

RET

+04:00

Reunion Island Time

SCT

+04:00

Mahe Island Time

AFT

+04:30

Kabul Time

AMST

+05:00

Armenia Summer Time (Yerevan)

AZST

+05:00

Azerbaijan Summer Time

GEST

+05:00

Georgia Summer Time

IOT

+05:00

Indian Chagos Time

KGT

+05:00

Kyrgyzstan Time

MVT

+05:00

Maldives Island Time

PKT

+05:00

Pakistan Time

TFT

+05:00

Kerguelen Time

TJT

+05:00

Tajikistan Time

TMT

+05:00

Turkmenistan Time

UZT

+05:00

Uzbekistan Time

YEKT

+05:00

Yekaterinburg Time

NPT

+05:45

Nepal Standard Time

ALMT

+06:00

Almaty Time

BDT

+06:00

Dacca Time

BTT

+06:00

Bhutan Time

DUSST

+06:00

Dushanbe Summer Time

KGST

+06:00

Kyrgyzstan Summer Time

LKT

+06:00

Lanka Time

MAWT

+06:00

Mawson, Antarctica

NOVT

+06:00

Novosibirsk Standard Time

OMST

+06:00

Omsk Time

UZST

+06:00

Uzbekistan Summer Time

YEKST

+06:00

Yekaterinburg Summer Time

CCT

+06:30

Indian Cocos (Island) Time

MMT

+06:30

Myanmar Time

ALMST

+07:00

Almaty Savings Time

CVT

+07:00

Christmas Island Time (Indian Ocean)

CXT

+07:00

Christmas Island Time (Indian Ocean)

DAVT

+07:00

Davis Time (Antarctica)

ICT

+07:00

Indochina Time

JAVT

+07:00

Java Time

KRAST

+07:00

Krasnoyarsk Summer Time

NOVST

+07:00

Novosibirsk Summer Time

OMSST

+07:00

Omsk Summer Time

WAST

+07:00

West Australian Std Time

JT

+07:30

Java Time

AWST

+08:00

Western Australia

BNT

+08:00

Brunei Darussalam Time

BORT

+08:00

Borneo Time (Indonesia)

CCT

+08:00

China Coast Time

HKT

+08:00

Hong Kong Time

IRKT

+08:00

Irkutsk Time

KRAT

+08:00

Krasnoyarsk Standard Time

MYT

+08:00

Malaysia Time

PHT

+08:00

Phillipine Time

ULAT

+08:00

Ulan Bator Time

WADT

+08:00

West Australian DST

WST

+08:00

West Australian Standard Time

MT

+08:30

Moluccas Time

AWSST

+09:00

Western Australia Time

IRKST

+09:00

Irkutsk Summer Time

JAYT

+09:00

Jayapura Time (Indonesia)

JST

+09:00

Japan Std Time, USSR Zone 8

KST

+09:00

Korea Standard Time

PWT

+09:00

Palau Time

ULAST

+09:00

Ulan Bator Summer Time

WDT

+09:00

West Australian DST

YAKT

+09:00

Yakutsk Time

ACST

+09:30

Central Australia

CAST

+09:30

Central Australian ST

SAST

+09:30

South Australian Std Time

SAT

+09:30

South Australian Std Time

AEST

+10:00

Australia Eastern Std Time

DDUT

+10:00

Dumont-d'Urville Time (Antarctica)

EAST

+10:00

East Australian Std Time

EST

+10:00

Australia Eastern Std Time

GST

+10:00

Guam Std Time, USSR Zone 9

KDT

+10:00

Korea Daylight Time

LIGT

+10:00

From Melbourne, Australia

MPT

+10:00

North Mariana Islands Time

PGT

+10:00

Papua New Guinea Time

trUK

+10:00

Truk Time

VLAT

+10:00

Vladivostok Time

YAKST

+10:00

Yakutsk Summer Time

YAPT

+10:00

Yap Time (Micronesia)

ACSST

+10:30

Central Australia Time

CADT

+10:30

Central Australian DST

CST

+10:30

Australia Central Std Time

LHST

+10:30

Lord Howe Standard Time, Australia

SADT

+10:30

South Australian Daylight Time

AESST

+11:00

Eastern Australia

LHDT

+11:00

Lord Howe Daylight Time, Australia

MAGT

+11:00

Magadan Time

NCT

+11:00

New Caledonia Time

PONT

+11:00

Ponape Time (Micronesia)

VLAST

+11:00

Vladivostok Summer Time

VUT

+11:00

Vanuata Time

ANAT

+12:00

Anadyr Time (Russia)

CKT

+12:00

Cook Islands Time

GILT

+12:00

Gilbert Islands Time

IDLE

+12:00

International Date Line, East

KOST

+12:00

Kosrae Time

MAGST

+12:00

Magadan Summer Time

MHT

+12:00

Kwajalein Time

NZST

+12:00

New Zealand Standard Time

NZT

+12:00

New Zealand Time

PETT

+12:00

Petropavlovsk-Kamchatski Time

TVT

+12:00

Tuvalu Time

WAKT

+12:00

Wake Time

WFT

+12:00

Wallis and Futuna Time

CHAST

+12:45

Chatham Island Time

ANAST

+13:00

Anadyr Summer Time (Russia)

NZDT

+13:00

New Zealand Daylight Time

PETST

+13:00

Petropavlovsk-Kamchatski Summer Time

PHOT

+13:00

Phoenix Islands (Kiribati) Time

TOT

+13:00

Tonga Time

CHADT

+13:45

Chatham Island Daylight Time

LINT

+14:00

Line Islands Time (Kiribati)

I mentioned earlier in this section that an INTERVAL value represents a time span. I also mentioned than an INTERVAL stores some number of seconds. The syntax for an INTERVAL literal allows you to specify the number of seconds in a variety of units.

The format of an INTERVAL value is

quantity unit [quantity unit ...][AGO]

The unit component specifies a number of seconds, as shown in Table 2.11. The quantity component acts as a multiplier (and may be fractional). If you have multiple quantity unit groups, they are all added together. The optional phrase AGO will cause the INTERVAL to be negative.

Table 2.11. INTERVAL Units

Description

Seconds

Unit Names

Microsecond[3]

.000001

us, usec, usecs, useconds, microsecon

Millisecond[3]

.001

-ms, msecs, mseconds, millisecon

Second

1

s, sec, secs, second, seconds

Minute

60

m, min, mins, minute, minutes

Hour

3600

h, hr, hrs, hours

Day

86400

d, day, days

Week

604800

w, week, weeks

Month (30 days)

2592000

mon, mons, month, months

Year

31557600

y, yr, yrs, year, years

Decade

315576000

dec, decs, decade, decades

Century

3155760000

c, cent, century, centuries

Millennium

31557600000

mil, mils, millennia, millennium

[3] Millisecond and microsecond can be used only in combination with another date/time component. For example, CAST( '1 SECOND 5000 MSEC' AS INTERVAL ) results in an interval of six seconds.

You can use the EXTRACT( EPOCH FROM interval ) function to convert an INTERVAL into a number of seconds. A few sample INTERVAL values are shown in Table 2.12. The Display column shows how PostgreSQL would format the Input Value for display. The EPOCH column shows the value that would be returned by extracting the EPOCH from the Input Value.

Table 2.12. Sample INTERVAL Values

Input Value

Display

EPOCH

.5 minutes

00:00:30

30

22 seconds 1 msec

00:00:22.00

22.001

22.001 seconds

00:00:22.00

22.001

10 centuries 2 decades

1020 years

32188752000

1 week 2 days 3.5 msec

9 days 00:00:00.00

777600.0035

 

Supported Operators

There are two types of operators that you can use with temporal values: arithmetic operators (addition and subtraction) and comparison operators.

You can add an INT4, a TIME, or a TIMETZ to a DATE. When you add an INT4, you are adding a number of days. Adding a TIME or TIMETZ to a DATE results in a TIMESTAMP. Table 2.13 lists the valid data type and operator combinations for temporal data types. The last column in Table 2.14 shows the data type of the resulting value.

Table 2.13. Arithmetic Date/Time Operators

Data Types

Valid Operators (q)

Result Type

DATE q DATE

-

INTEGER

DATE q TIME

+

TIMESTAMP

DATE q TIMETZ

+

TIMESTAMP WITH TIMEZONE

DATE q INT4

+ -

DATE

TIME q DATE

+

TIMESTAMP

TIME q INTERVAL

+ -

TIME

TIMETZ q DATE

+

TIMESTAMP WITH TIMEZONE

TIMETZ q INTERVAL

+ -

TIMETZ

TIMESTAMP q TIMESTAMP

-

INTERVAL

TIMESTAMP q INTERVAL

+ -

TIMESTAMP WITH TIMEZONE

INTERVAL q TIME

+

TIME WITHOUT TIMEZONE

Table 2.14. Arithmetic Date/Time Operator Examples

Example

Result

'23-JAN-2003'::DATE - '23-JAN-2002'::DATE

365

'23-JAN-2003'::DATE + '2:35 PM'::TIME

2003-01-23 14:35:00

'23-JAN-2003'::DATE + '2:35 PM GMT'::TIMETZ

2003-01-23 09:35:00-05

'23-JAN-2003'::DATE + 2::INT4

2003-01-25

'2:35 PM'::TIME + '23-JAN-2003'::DATE

2003-01-23 14:35:00

'2:35 PM'::TIME + '2 hours 5 minutes'::INTERVAL

16:40:00

'2:35 PM EST'::TIMETZ + '23-JAN-2003'::DATE

2003-01-23 14:35:00-05

'2:35 PM EST'::TIMETZ + '2 hours 5 minutes'::INTERVAL

16:40:00-05

'23-JAN-2003 2:35 PM EST'::TIMESTAMP - '23-JAN-2002 1:00 PM EST'::TIMESTAMP

365 days 01:35

'23-JAN-2003 2:35 PM EST'::TIMESTAMP + '3 days 2 hours 5 minutes'::INTERVAL

2003-01-26 16:40:00-05

'2 hours 5 minutes'::INTERVAL + '2:34 PM'::TIME

16:39:00

Table 2.14 shows how each of the arithmetic operators behave when applied to date/time values.

Using the temporal comparison operators, you can determine the relationship between two date/time values. For purposes of comparison, an earlier date/time value is considered to be less than a later date/time value.

Table 2.15 shows how you can combine the various temporal types with comparison operators.

Table 2.15. Date/Time Comparison Operators

Data Types

Valid Operators (q)

date q date

< <= <> = >= >

time q time

< <= <> = >= >

timetz q timetz

< <= <> = >= >

timestamp q timestamp

< <= <> = >= >


Part I: General PostgreSQL Use

Introduction to PostgreSQL and SQL

Working with Data in PostgreSQL

PostgreSQL SQL Syntax and Use

Performance

Part II: Programming with PostgreSQL

Introduction to PostgreSQL Programming

Extending PostgreSQL

PL/pgSQL

The PostgreSQL C APIlibpq

A Simpler C APIlibpgeasy

The New PostgreSQL C++ APIlibpqxx

Embedding SQL Commands in C Programsecpg

Using PostgreSQL from an ODBC Client Application

Using PostgreSQL from a Java Client Application

Using PostgreSQL with Perl

Using PostgreSQL with PHP

Using PostgreSQL with Tcl and Tcl/Tk

Using PostgreSQL with Python

Npgsql: The .NET Data Provider

Other Useful Programming Tools

Part III: PostgreSQL Administration

Introduction to PostgreSQL Administration

PostgreSQL Administration

Internationalization and Localization

Security

Replicating PostgreSQL Data with Slony

Contributed Modules

Index



PostgreSQL(c) The comprehensive guide to building, programming, and administering PostgreSQL databases
PostgreSQL(c) The comprehensive guide to building, programming, and administering PostgreSQL databases
ISBN: 735712573
EAN: N/A
Year: 2004
Pages: 261

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