Date/Time Functions and Operators

Date/Time Functions and Operators

Date/Time Functions shows the available functions for date/time value processing, with details appearing in the following subsections. Date/Time Operators illustrates the behaviors of the basic arithmetic operators (+, *, etc.). For formatting functions, refer to Data Type Formatting Functions. You should be familiar with the background information on date/time data types from Date/Time Types.

In addition, the usual comparison operators shown in Comparison Operators are available for the date/time types. Dates and timestamps (with or without time zone) are all comparable, while times (with or without time zone) and intervals can only be compared to other values of the same data type. When comparing a timestamp without time zone to a timestamp with time zone, the former value is assumed to be given in the time zone specified by the TimeZone configuration parameter, and is rotated to UTC for comparison to the latter value (which is already in UTC internally). Similarly, a date value is assumed to represent midnight in the TimeZone zone when comparing it to a timestamp.

All the functions and operators described below that take time or timestamp inputs actually come in two variants: one that takes time with time zone or timestamp with time zone, and one that takes time without time zone or timestamp without time zone. For brevity, these variants are not shown separately. Also, the + and * operators come in commutative pairs (for example both date + integer and integer + date); we show only one of each such pair.

Table: Date/Time Operators

Table: Date/Time Functions

In addition to these functions, the SQL OVERLAPS operator is supported:

(START1, END1) OVERLAPS (START2, END2)
(START1, LENGTH1) OVERLAPS (START2, LENGTH2)

SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS
       (DATE '2001-10-30', DATE '2002-10-30');
Result: true
SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
       (DATE '2001-10-30', DATE '2002-10-30');
Result: false
SELECT (DATE '2001-10-29', DATE '2001-10-30') OVERLAPS
       (DATE '2001-10-30', DATE '2001-10-31');
Result: false
SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS
       (DATE '2001-10-30', DATE '2001-10-31');
Result: true

When adding an interval value to (or subtracting an interval value from) a timestamp or timestamp with time zone value, the months, days, and microseconds fields of the interval value are handled in turn. First, a nonzero months field advances or decrements the date of the timestamp by the indicated number of months, keeping the day of month the same unless it would be past the end of the new month, in which case the last day of that month is used. (For example, March 31 plus 1 month becomes April 30, but March 31 plus 2 months becomes May 31.) Then the days field advances or decrements the date of the timestamp by the indicated number of days. In both these steps the local time of day is kept the same. Finally, if there is a nonzero microseconds field, it is added or subtracted literally. When doing arithmetic on a timestamp with time zone value in a time zone that recognizes DST, this means that adding or subtracting (say) interval '1 day' does not necessarily have the same result as adding or subtracting interval '24 hours'. For example, with the session time zone set to America/Denver:

SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '1 day';
Result: 2005-04-03 12:00:00-06
SELECT timestamp with time zone '2005-04-02 12:00:00-07' + interval '24 hours';
Result: 2005-04-03 13:00:00-06

Note there can be ambiguity in the months field returned by age because different months have different numbers of days. PostgreSQL's approach uses the month from the earlier of the two dates when calculating partial months. For example, age('2004-06-01', '2004-04-30') uses April to yield 1 mon 1 day, while using May would yield 1 mon 2 days because May has 31 days, while April has only 30.

Subtraction of dates and timestamps can also be complex. One conceptually simple way to perform subtraction is to convert each value to a number of seconds using EXTRACT(EPOCH FROM ...), then subtract the results; this produces the number of seconds between the two values. This will adjust for the number of days in each month, timezone changes, and daylight saving time adjustments. Subtraction of date or timestamp values with the “-” operator returns the number of days (24-hours) and hours/minutes/seconds between the values, making the same adjustments. The age function returns years, months, days, and hours/minutes/seconds, performing field-by-field subtraction and then adjusting for negative field values. The following queries illustrate the differences in these approaches. The sample results were produced with timezone = 'US/Eastern'; there is a daylight saving time change between the two dates used:

SELECT EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
       EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00');
Result: 10537200.000000
SELECT (EXTRACT(EPOCH FROM timestamptz '2013-07-01 12:00:00') -
        EXTRACT(EPOCH FROM timestamptz '2013-03-01 12:00:00'))
        / 60 / 60 / 24;
Result: 121.9583333333333333
SELECT timestamptz '2013-07-01 12:00:00' - timestamptz '2013-03-01 12:00:00';
Result: 121 days 23:00:00
SELECT age(timestamptz '2013-07-01 12:00:00', timestamptz '2013-03-01 12:00:00');
Result: 4 mons

EXTRACT, date_part

EXTRACT(FIELD FROM SOURCE)

The extract function retrieves subfields such as year or hour from date/time values. source must be a value expression of type timestamp, date, time, or interval. (Timestamps and times can be with or without time zone.) field is an identifier or string that selects what field to extract from the source value. Not all fields are valid for every input data type; for example, fields smaller than a day cannot be extracted from a date, while fields of a day or more cannot be extracted from a time. The extract function returns values of type numeric.

The following are valid field names:

century : The century; for interval values, the year field divided by 100

```

SELECT EXTRACT(CENTURY FROM TIMESTAMP '2000-12-16 12:21:13');
Result: 20
SELECT EXTRACT(CENTURY FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 21
SELECT EXTRACT(CENTURY FROM DATE '0001-01-01 AD');
Result: 1
SELECT EXTRACT(CENTURY FROM DATE '0001-12-31 BC');
Result: -1
SELECT EXTRACT(CENTURY FROM INTERVAL '2001 years');
Result: 20
```

day : The day of the month (1–31); for interval values, the number of days

```

SELECT EXTRACT(DAY FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 16
SELECT EXTRACT(DAY FROM INTERVAL '40 days 1 minute');
Result: 40
```

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 as Sunday (0) to Saturday (6)

```

SELECT EXTRACT(DOW FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 5
```


 Note that `extract`'s day of the week numbering differs from that of the `to_char(..., 'D')` function.

doy : The day of the year (1–365/366)

```

SELECT EXTRACT(DOY FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 47
```

epoch : For timestamp with time zone values, the number of seconds since 1970-01-01 00:00:00 UTC (negative for timestamps before that); for date and timestamp values, the nominal number of seconds since 1970-01-01 00:00:00, without regard to timezone or daylight-savings rules; for interval values, the total number of seconds in the interval

```

SELECT EXTRACT(EPOCH FROM TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40.12-08');
Result: 982384720.120000
SELECT EXTRACT(EPOCH FROM TIMESTAMP '2001-02-16 20:38:40.12');
Result: 982355920.120000
SELECT EXTRACT(EPOCH FROM INTERVAL '5 days 3 hours');
Result: 442800.000000
```


 You can convert an epoch value back to a `timestamp with time zone` with `to_timestamp`:


```

SELECT to_timestamp(982384720.12);
Result: 2001-02-17 04:38:40.12+00
```


 Beware that applying `to_timestamp` to an epoch extracted from a `date` or `timestamp` value could produce a misleading result: the result will effectively assume that the original value had been given in UTC, which might not be the case.

hour : The hour field (0–23 in timestamps, unrestricted in intervals)

```

SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 20
```

isodow : The day of the week as Monday (1) to Sunday (7)

```

SELECT EXTRACT(ISODOW FROM TIMESTAMP '2001-02-18 20:38:40');
Result: 7
```


 This is identical to `dow` except for Sunday. This matches the ISO 8601 day of the week numbering.

isoyear : The ISO 8601 week-numbering year that the date falls in

```

SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-01');
Result: 2005
SELECT EXTRACT(ISOYEAR FROM DATE '2006-01-02');
Result: 2006
```


 Each ISO 8601 week-numbering year begins with the Monday of the week containing the 4th of January, so in early January or late December the ISO year may be different from the Gregorian year. See the `week` field for more information.

julian : The Julian Date corresponding to the date or timestamp. Timestamps that are not local midnight result in a fractional value. See Julian Dates for more information.

```

SELECT EXTRACT(JULIAN FROM DATE '2006-01-01');
Result: 2453737
SELECT EXTRACT(JULIAN FROM TIMESTAMP '2006-01-01 12:00');
Result: 2453737.50000000000000000000
```

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 millennium; for interval values, the year field divided by 1000

```

SELECT EXTRACT(MILLENNIUM FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 3
SELECT EXTRACT(MILLENNIUM FROM INTERVAL '2001 years');
Result: 2
```


 Years in the 1900s are in the second millennium. The third millennium started January 1, 2001.

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: 28500.000
```

minute : The minutes field (0–59)

```

SELECT EXTRACT(MINUTE FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 38
```

month : 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 date is in; for interval values, the month field divided by 3 plus 1

```

SELECT EXTRACT(QUARTER FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 1
SELECT EXTRACT(QUARTER FROM INTERVAL '1 year 6 months');
Result: 3
```

second : The seconds field, including any fractional seconds

```

SELECT EXTRACT(SECOND FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 40.000000
SELECT EXTRACT(SECOND FROM TIME '17:12:28.5');
Result: 28.500000
```

timezone : The time zone offset from UTC, measured in seconds. Positive values correspond to time zones east of UTC, negative values to zones west of UTC. (Technically, PostgreSQL does not use UTC because leap seconds are not handled.)

timezone_hour : The hour component of the time zone offset

timezone_minute : The minute component of the time zone offset

week : The number of the ISO 8601 week-numbering week of the year. By definition, ISO weeks start on Mondays and the first week of a year contains January 4 of that year. In other words, the first Thursday of a year is in week 1 of that year.

 In the ISO week-numbering system, it is possible for early-January dates to be part of the 52nd or 53rd week of the previous year, and for late-December dates to be part of the first week of the next year. For example, `2005-01-01` is part of the 53rd week of year 2004, and `2006-01-01` is part of the 52nd week of year 2005, while `2012-12-31` is part of the first week of 2013. It's recommended to use the `isoyear` field together with `week` to get consistent results.


 For `interval` values, the week field is simply the number of integral days divided by 7.


```

SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 7
SELECT EXTRACT(WEEK FROM INTERVAL '13 days 24 hours');
Result: 1
```

year : The year field. Keep in mind there is no 0 AD, so subtracting BC years from AD years should be done with care.

```

SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
Result: 2001
```

When processing an interval value, the extract function produces field values that match the interpretation used by the interval output function. This can produce surprising results if one starts with a non-normalized interval representation, for example:

SELECT INTERVAL '80 minutes';
Result: 01:20:00
SELECT EXTRACT(MINUTES FROM INTERVAL '80 minutes');
Result: 20

The extract function is primarily intended for computational processing. For formatting date/time values for display, see Data Type Formatting Functions.

The date_part function is modeled on the traditional Ingres equivalent to the SQL-standard function extract:

date_part('FIELD', SOURCE)

SELECT date_part('day', TIMESTAMP '2001-02-16 20:38:40');
Result: 16
SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
Result: 4

date_trunc

The function date_trunc is conceptually similar to the trunc function for numbers.

date_trunc(FIELD, SOURCE [, TIME_ZONE ])

Valid values for field are:

• microseconds
• milliseconds
• second
• minute
• hour
• day
• week
• month
• quarter
• year
• decade
• century
• millennium

When the input value is of type timestamp with time zone, the truncation is performed with respect to a particular time zone; for example, truncation to day produces a value that is midnight in that zone. By default, truncation is done with respect to the current TimeZone setting, but the optional time_zone argument can be provided to specify a different time zone. The time zone name can be specified in any of the ways described in Time Zones.

A time zone cannot be specified when processing timestamp without time zone or interval inputs. These are always taken at face value.

Examples (assuming the local time zone is America/New_York):

SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-02-16 20:00:00
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-01-01 00:00:00
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00');
Result: 2001-02-16 00:00:00-05
SELECT date_trunc('day', TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40+00', 'Australia/Sydney');
Result: 2001-02-16 08:00:00-05
SELECT date_trunc('hour', INTERVAL '3 days 02:47:33');
Result: 3 days 02:00:00

date_bin

The function date_bin “bins” the input timestamp into the specified interval (the stride) aligned with a specified origin.

date_bin(STRIDE, SOURCE, ORIGIN)

Examples:

SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01');
Result: 2020-02-11 15:30:00
SELECT date_bin('15 minutes', TIMESTAMP '2020-02-11 15:44:17', TIMESTAMP '2001-01-01 00:02:30');
Result: 2020-02-11 15:32:30

In the case of full units (1 minute, 1 hour, etc.), it gives the same result as the analogous date_trunc call, but the difference is that date_bin can truncate to an arbitrary interval.

The stride interval must be greater than zero and cannot contain units of month or larger.

AT TIME ZONE and AT LOCAL

The AT TIME ZONE operator converts time stamp without time zone to/from time stamp with time zone, and time with time zone values to different time zones. AT TIME ZONE and AT LOCAL Variants shows its variants.

Table: AT TIME ZONE and AT LOCAL Variants

In these expressions, the desired time zone zone can be specified either as a text value (e.g., 'America/Los_Angeles') or as an interval (e.g., INTERVAL '-08:00'). In the text case, a time zone name can be specified in any of the ways described in Time Zones. The interval case is only useful for zones that have fixed offsets from UTC, so it is not very common in practice.

The syntax AT LOCAL may be used as shorthand for AT TIME ZONE local, where local is the session's TimeZone value.

Examples (assuming the current TimeZone setting is America/Los_Angeles):

SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'America/Denver';
Result: 2001-02-16 19:38:40-08
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'America/Denver';
Result: 2001-02-16 18:38:40
SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'Asia/Tokyo' AT TIME ZONE 'America/Chicago';
Result: 2001-02-16 05:38:40
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT LOCAL;
Result: 2001-02-16 17:38:40
SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE '+05';
Result: 2001-02-16 20:38:40
SELECT TIME WITH TIME ZONE '20:38:40-05' AT LOCAL;
Result: 17:38:40

The sixth example is a cautionary tale. Due to the fact that there is no date associated with the input value, the conversion is made using the current date of the session. Therefore, this static example may show a wrong result depending on the time of the year it is viewed because 'America/Los_Angeles' observes Daylight Savings Time.

The function timezone(zone, timestamp) is equivalent to the SQL-conforming construct timestamp AT TIME ZONE zone.

The function timezone(zone, time) is equivalent to the SQL-conforming construct time AT TIME ZONE zone.

The function timezone(timestamp) is equivalent to the SQL-conforming construct timestamp AT LOCAL.

The function timezone(time) is equivalent to the SQL-conforming construct time AT LOCAL.

Current Date/Time

PostgreSQL provides a number of functions that return values related to the current date and time. These SQL-standard functions all return values based on the start time of the current transaction:

CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME(PRECISION)
CURRENT_TIMESTAMP(PRECISION)
LOCALTIME
LOCALTIMESTAMP
LOCALTIME(PRECISION)
LOCALTIMESTAMP(PRECISION)

CURRENT_TIME and CURRENT_TIMESTAMP deliver values with time zone; LOCALTIME and LOCALTIMESTAMP deliver values without time zone.

CURRENT_TIME, CURRENT_TIMESTAMP, LOCALTIME, and LOCALTIMESTAMP can optionally take a precision parameter, which causes the result to be rounded to that many fractional digits in the seconds field. Without a precision parameter, the result is given to the full available precision.

Some examples:

SELECT CURRENT_TIME;
Result: 14:39:53.662522-05
SELECT CURRENT_DATE;
Result: 2019-12-23
SELECT CURRENT_TIMESTAMP;
Result: 2019-12-23 14:39:53.662522-05
SELECT CURRENT_TIMESTAMP(2);
Result: 2019-12-23 14:39:53.66-05
SELECT LOCALTIMESTAMP;
Result: 2019-12-23 14:39:53.662522

Since these functions return the start time of the current transaction, their values do not change during the transaction. This is considered a feature: the intent is to allow a single transaction to have a consistent notion of the “current” time, so that multiple modifications within the same transaction bear the same time stamp.

PostgreSQL also provides functions that return the start time of the current statement, as well as the actual current time at the instant the function is called. The complete list of non-SQL-standard time functions is:

transaction_timestamp()
statement_timestamp()
clock_timestamp()
timeofday()
now()

transaction_timestamp() is equivalent to CURRENT_TIMESTAMP, but is named to clearly reflect what it returns. statement_timestamp() returns the start time of the current statement (more specifically, the time of receipt of the latest command message from the client). statement_timestamp() and transaction_timestamp() return the same value during the first statement of a transaction, but might differ during subsequent statements. clock_timestamp() returns the actual current time, and therefore its value changes even within a single SQL statement. timeofday() is a historical PostgreSQL function. Like clock_timestamp(), it returns the actual current time, but as a formatted text string rather than a timestamp with time zone value. now() is a traditional PostgreSQL equivalent to transaction_timestamp().

All the date/time data types also accept the special literal value now to specify the current date and time (again, interpreted as the transaction start time). Thus, the following three all return the same result:

SELECT CURRENT_TIMESTAMP;
SELECT now();
SELECT TIMESTAMP 'now';  -- but see tip below

Delaying Execution

The following functions are available to delay execution of the server process:

pg_sleep ( double precision )
pg_sleep_for ( interval )
pg_sleep_until ( timestamp with time zone )

SELECT pg_sleep(1.5);
SELECT pg_sleep_for('5 minutes');
SELECT pg_sleep_until('tomorrow 03:00');