+ linkend="datatype-datetime">).
Date/Time Functions
|
- Function
- Returns
+ Name
+ Return Type
Description
Example
+ Result
+
- |
- abstime(timestamp)
- abstime
- convert to abstime
- abstime(timestamp 'now')
-
+
+
|
age(timestamp)
interval
- preserve months and years
+ Subtract argument from current date, preserve years and months and days
age(timestamp '1957-06-13')
+ 43 years 8 mons 3 days
+
|
- age(timestamp,timestamp)
+ age(timestamp, timestamp)
interval
preserve months and years
age('now', timestamp '1957-06-13')
+
+]]>
+
|
- date_part(text,timestamp)
+ current_date
+ date
+
+ returns current date; see also
+ linkend="functions-datetime-current">below
+
+
+
+
+
+ |
+ current_time
+ time
+
+ returns current time (of day); see also
+ linkend="functions-datetime-current">below
+
+
+
+
+
+ |
+ current_timestamp
+ timestamp
+
+ returns current date and time; see also
+ linkend="functions-datetime-current">below
+
+
+
+
+
+ |
+ date_part(text, timestamp)
double precision
- portion of date
- date_part('dow',timestamp 'now')
+
+ extract subfield from date/time value (equivalent to
+
extract); see also
+ linkend="functions-datetime-datepart">below
+
+ date_part('hour', timestamp '2001-02-16 20:38:40')
+ 20
+
|
- date_part(text,interval)
+ date_part(text, interval)
double precision
- portion of time
- date_part('hour',interval '4 hrs 3 mins')
+
+ extract subfield from interval value (equivalent to
+
extract); see also
+ linkend="functions-datetime-datepart">below
+
+ date_part('month', interval '2 years 3 months')
+ 3
+
|
- date_trunc(text,timestamp)
+ date_trunc(text, timestamp)
timestamp
- truncate date
- date_trunc('month',abstime 'now')
+
+ truncate date to specified precision; see also
+ linkend="functions-datetime-trunc">below
+
+ date_trunc('hour', timestamp '2001-02-16 20:38:40')
+ 2001-02-16 20:00:00+00
+
|
- interval(reltime)
- interval
- convert to interval
- interval(reltime '4 hours')
+ extract(identifier from timestamp)
+ double precision
+
+ extract subfield from date/time value; see also
+ linkend="functions-datetime-extract">below
+
+ extract(hour from timestamp '2001-02-16 20:38:40')
+ 20
+
+ |
+ extract(identifier from interval)
+ double precision
+
+ extract subfield from interval value; see also
+ linkend="functions-datetime-extract">below
+
+ extract(month from interval '2 years 3 months')
+ 3
+
+
|
isfinite(timestamp)
- bool
- a finite time?
- isfinite(timestamp 'now')
+ boolean
+ Returns true if the time stamp is finite (neither invalid nor infinity)
+ isfinite(timestamp '2001-02-16 21:28:30')
+ true
+
|
isfinite(interval)
- bool
- a finite time?
- isfinite(interval '4 hrs')
+ boolean
+ Returns true if the interval is finite in length
+ isfinite(interval '4 hours')
+ true
+
|
- reltime(interval)
- reltime
- convert to reltime
- reltime(interval '4 hrs')
+ now()
+ timestamp
+
+ returns current date and time (equivalent to
+
current_timestamp); see also
+ linkend="functions-datetime-current">below
+
+
+
+
|
timestamp(date)
timestamp
- convert to timestamp
- timestamp(date 'today')
+ convert date to timestamp
+ timestamp(date '2000-12-25')
+ 2000-12-25 00:00:00
+
|
- timestamp(date,time)
+ timestamp(date, time)
timestamp
- convert to timestamp
- timestamp(timestamp '1998-02-24',time '23:07');
-
- |
- to_char(timestamp,text)
- text
- convert to string
- to_char(timestamp '1998-02-24','DD');
+ combine date and time into a timestamp
+ timestamp(date '1998-02-24',time '23:07')
+ 1998-02-24 23:07:00
+
+
+
+
<function>EXTRACT</function>, <function>date_part</function>
+
+
+EXTRACT (field FROM source)
+
+
+ The extract function retrieves sub-fields
+ from date/time values, such as year or hour.
+ source is a value expression that
+ evaluates to type timestamp or interval.
+ (Expressions of type date or time will
+ be cast to timestamp and can therefore be used as
+ well.) field is an identifier (not a
+ string!) that selects what field to extract from the source value.
+ The extract function returns values of type
+ double precision.
+ The following are valid values:
+
+
+
+
+ century
+
+ The year field divided by 100
+
+
+
+
+SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 20
+
+
+
+ Note that this is not really the century that the date is in.
+
+
+
+
+
+ day
+
+ The day (of the month) field (1 - 31)
+
+
+
+
+SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 16
+
+
+
+
+
+
+ decade
+
+ The year field divided by 10
+
+
+
+
+SELECT EXTRACT(DECADE FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 200
+
+
+
+
+
+
+ dow
+
+ The day of the week (0 - 6; Sunday is 0) (for
+ timestamp values only)
+
+
+
+
+SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 5
+
+
+
+
+
+
+ doy
+
+ The day of the year (1 - 365/366) (for timestamp values only)
+
+
+
+SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 47
+
+
+
+
+
+
+ epoch
+
+ For date and timestamp values, the
+ number of seconds since 1970-01-01 00:00:00 (Result may be
+ negative.); for interval values, the total number
+ of seconds in the interval
+
+
+
+
+SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 982352320
+
+SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
+Result: 442800
+
+
+
+
+
+
+ hour
+
+ The hour field (0 - 23)
+
+
+
+
+SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 20
+
+
+
+
+
+
+ microseconds
+
+ The seconds field, including fractional parts, multiplied by 1
+ 000 000. Note that this includes full seconds.
+
+
+
+
+SELECT EXTRACT(MICROSECONDS FROM TIME '17:12:28.5');
+Result: 28500000
+
+
+
+
+
+
+ millennium
+
+ The year field divided by 1000
+
+
+
+
+SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 2
+
+
+
+ Note that this is not really the millennium that the date is in.
+
+
+
+
+
+ milliseconds
+
+ The seconds field, including fractional parts, multiplied by
+ 1000. Note that this includes full seconds.
+
+
+
+
+SELECT EXTRACT(MILLISECONDS FROM TIME '17:12:28.5');
+Result: 28500
+
+
+
+
+
+
+ minute
+
+ The minutes field (0 - 59)
+
+
+
+
+SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 38
+
+
+
+
+
+
+ month
+
+ For timestamp values, the number of the month
+ within the year (1 - 12) ; for interval values
+ the number of months, modulo 12 (0 - 11)
+
+
+
+
+SELECT EXTRACT(MONTH FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 2
+
+SELECT EXTRACT(MONTH FROM INTERVAL '2 years 3 months');
+Result: 3
+
+SELECT EXTRACT(MONTH FROM INTERVAL '2 years 13 months');
+Result: 1
+
+
+
+
+
+
+ quarter
+
+ The quarter of the year (1 - 4) that the day is in (for
+ timestamp values only)
+
+
+
+
+SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 1
+
+
+
+
+
+
+ second
+
+ The seconds field, including fractional parts (0 -
+ 5960 if leap seconds are
+ implemented by the operating system)
+
+
+
+
+SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 40
+
+SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
+Result: 28.5
+
+
+
+
+
+
+ week
+
+ From a timestamp value, calculate the number of
+ the week of the year that the day is in. By definition
+ (
ISO 8601), the first week of a year
+ contains January 4 of that year. (The
ISO+ week starts on Monday.) In other words, the first Thursday of
+ a year is in week 1 of that year.
+
+
+
+
+SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 7
+
+
+
+
+
+
+ year
+
+ The year field
+
+
+
+
+SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
+Result: 2001
+
+
+
+
+
+
+
+
+
- For the
- date_part and date_trunc
- functions, arguments can be
- `year', `month',
- `day', `hour',
- `minute', and `second',
- as well as the more specialized quantities
- `decade', `century',
- `millennium', `millisecond',
- and `microsecond'.
- date_part allows `dow'
- to return day of week, 'week' to return the
- ISO-defined week of year, and `epoch' to return
- seconds since 1970 (for timestamp)
- or 'epoch' to return total elapsed seconds
- (for interval).
+ The extract function is primarily intended
+ for computational processing. For formatting date/time values for
+ display, see .
-
+
+ The date_part function is the traditional
+
Postgres equivalent to the
+
+date_part('field', source)
+
+ Note that here the field value needs to
+ be a string. The valid field values for
+ date_part are the same as for
+ extract.
+
+
+
+
+SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
+Result: 16
+
+SELECT date_part('hour', INTERVAL '4 hours 3 minutes')
+Result: 4
+
+
+
+
+
+
+
<function>date_trunc</function>
+
+ The function date_trunc is conceptually
+ similar to the trunc function for numbers.
+
+
+
+date_trunc('field', source)
+
+ source is a value expression of type
+ timestamp (values of type date and
+ time are cast automatically).
+ field selects to which precision to
+ truncate the time stamp value. The return value is of type
+ timestamp with all fields that are less than the
+ selected one set to zero (or one, for day and month).
+
+
+ Valid values for field are:
+
+ microseconds
+ milliseconds
+ second
+ minute
+ hour
+ day
+ month
+ year
+ decade
+ century
+ millennium
+
+
+
+
+
+SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
+Result: 2001-02-16 20:00:00+00
+
+SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
+Result: 2001-01-01 00:00:00+00
+
+
+
+
+
+
+
Current Date/Time
+
+ The following functions are available to select the current date and/or time:
+
+CURRENT_TIME
+CURRENT_DATE
+CURRENT_TIMESTAMP
+
+ Note that because of the requirements of the
+
SQL standard, these functions must not be
+ called with trailing parentheses.
+
+
+
+
+SELECT CURRENT_TIME;
+19:07:13
+
+SELECT CURRENT_DATE;
+2001-02-17
+
+SELECT CURRENT_TIMESTAMP;
+2001-02-17 19:07:32+00
+
+
+
+ The function now() is the traditional
+ CURRENT_TIMESTAMP.
+
Postgres furthermore has special
+ date/time constants
that can be used to specify the
+ current time. The following three all return the same result:
+SELECT CURRENT_TIMESTAMP;
+SELECT now();
+SELECT TIMESTAMP 'now';
+
+
+ You do not want to use the third form when specifying a DEFAULT
+ value when creating a table. The system will immediately
+ evaluate the constant, thus when the default value is needed,
+ the time of the table creation would be used! The first two
+ forms will not be evaluated until the default value is used,
+ because they are function calls.
+
+
+
+
+
|
isclosed(path)
- bool
+ boolean
a closed path?
isclosed(path '((0,0),(1,1),(2,0))')
|
isopen(path)
- bool
+ boolean
an open path?
isopen(path '[(0,0),(1,1),(2,0)]')
Conditional Expressions
- This section descibes the SQL-compliant conditional expressions
+ This section desc
ribes the SQL-compliant conditional expressions
The
SQL CASE expression is a
generic conditional expression, similar to if/else statements in
- other languages. CASE clauses can be used whereever
+ other languages. CASE clauses can be used wherever
an expression is valid. condition is an
- expression that returns a boolean result. If the result is true
+ expression that returns a boolean result. If the result is true
then the value of the CASE expression is
result. If the result is false any
subsequent WHEN clauses are searched in the same
projects / postgresql.git / commitdiff