凋零的羽

Date And Time Functions

SQLite supports five date and time functions as follows:

1. date(timestring, modifier, modifier, …)
2. time(timestring, modifier, modifier, …)
3. datetime(timestring, modifier, modifier, …)
4. julianday(timestring, modifier, modifier, …)
5. strftime(format, timestring, modifier, modifier, …)

All five date and time functions take a time string as an argument. The time string is followed by zero or more modifiers. The strftime() function also takes a format string as its first argument.

The date and time functions use a subset of IS0-8601 date and time formats. The date() function returns the date in this format: YYYY-MM-DD. The time() function returns the time as HH:MM:SS. The datetime() function returns “YYYY-MM-DD HH:MM:SS”. The julianday() function returns the Julian day - the number of days since noon in Greenwich on November 24, 4714 B.C. (Proleptic Gregorian calendar). The strftime() routine returns the date formatted according to the format string specified as the first argument. The format string supports the most common substitutions found in the strftime() function from the standard C library plus two new substitutions, %f and %J. The following is a complete list of valid strftime() substitutions:

%d		day of month: 00
%f		fractional seconds: SS.SSS
%H		hour: 00-24
%j		day of year: 001-366
%J		Julian day number
%m		month: 01-12
%M		minute: 00-59
%s		seconds since 1970-01-01
%S		seconds: 00-59
%w		day of week 0-6 with Sunday==0
%W		week of year: 00-53
%Y		year: 0000-9999
%%		%

Notice that all other date and time functions can be expressed in terms of strftime():

Function		Equivalent strftime()
date(…)		strftime(‘%Y-%m-%d’, …)
time(…)		strftime(‘%H:%M:%S’, …)
datetime(…)		strftime(‘%Y-%m-%d %H:%M:%S’, …)
julianday(…)		strftime(‘%J’, …)

The only reasons for providing functions other than strftime() is for convenience and for efficiency.

Time Strings

A time string can be in any of the following formats:

1. YYYY-MM-DD
2. YYYY-MM-DD HH:MM
3. YYYY-MM-DD HH:MM:SS
4. YYYY-MM-DD HH:MM:SS.SSS
5. YYYY-MM-DDTHH:MM
6. YYYY-MM-DDTHH:MM:SS
7. YYYY-MM-DDTHH:MM:SS.SSS
8. HH:MM
9. HH:MM:SS
10. HH:MM:SS.SSS
11. now
12. DDDDDDDDDD

In formats 5 through 7, the “T” is a literal character separating the date and the time, as required by ISO-8601. Formats 8 through 10 that specify only a time assume a date of 2000-01-01. Format 11, the string ‘now’, is converted into the current date and time as obtained from the xCurrentTime method of the sqlite3_vfs object in use. Universal Coordinated Time (UTC) is used. Format 12 is the Julian day numberexpressed as a floating point value.

Modifiers

The time string can be followed by zero or more modifiers that alter date and/or time. Each modifier is a transformation that is applied to the time value to its left. Modifiers are applied from left to right; order is important. The available modifiers are as follows.

1. NNN days
2. NNN hours
3. NNN minutes
4. NNN.NNNN seconds
5. NNN months
6. NNN years
7. start of month
8. start of year
9. start of day
10. weekday N
11. unixepoch
12. localtime
13. utc

The first six modifiers (1 through 6) simply add the specified amount of time to the date and time specified by the preceding timestring and modifiers. Note that “±NNN months” works by rendering the original date into the YYYY-MM-DD format, adding the ±NNN to the MM month value, then normalizing the result. Thus, for example, the data 2001-03-31 modified by ‘+1 month’ initially yields 2001-04-31, but April only has 30 days so the date is normalized to 2001-05-01. A similar effect occurs when the original date is February 29 of a leapyear and the modifier is ±N years where N is not a multiple of four.

The “start of” modifiers (7 through 9) shift the date backwards to the beginning of the current month, year or day.

The “weekday” modifier advances the date forward to the next date where the weekday number is N. Sunday is 0, Monday is 1, and so forth.

The “unixepoch” modifier (11) only works if it immediately follows a timestring in the DDDDDDDDDD format. This modifier causes the DDDDDDDDDD to be interpreted not as a Julian day number as it normally would be, but as Unix Time - the number of seconds since 1970. If the “unixepoch” modifier does not follow a timestring of the form DDDDDDDDDD which expresses the number of seconds since 1970 or if other modifiers separate the “unixepoch” modifier from prior DDDDDDDDDD then the behavior is undefined. Due to precision limitations imposed by the implementations use of 64-bit integers, the “unixepoch” modifier only works for dates between 0000-01-01 00:00:00 and 5352-11-01 10:52:47 (unix times of -62167219200 through 10675199167).

The “localtime” modifier (12) assumes the time string to its left is in Universal Coordinated Time (UTC) and adjusts the time string so that it displays localtime. If “localtime” follows a time that is not UTC, then the behavior is undefined. The “utc” is the opposite of “localtime”. “utc” assumes that the string to its left is in the local timezone and adjusts that string to be in UTC. If the prior string is not in localtime, then the result of “utc” is undefined.

Examples

Compute the current date.

SELECT date(‘now’);

Compute the last day of the current month.

SELECT date(‘now’,'start of month’,'+1 month’,'-1 day’);

Compute the date and time given a unix timestamp 1092941466.

SELECT datetime(1092941466, ‘unixepoch’);

Compute the date and time given a unix timestamp 1092941466, and compensate for your local timezone.

SELECT datetime(1092941466, ‘unixepoch’, ‘localtime’);

Compute the current unix timestamp.

SELECT strftime(‘%s’,'now’);

Compute the number of days since the signing of the US Declaration of Independence.

SELECT julianday(‘now’) – julianday(’1776-07-04′);

Compute the number of seconds since a particular moment in 2004:

SELECT strftime(‘%s’,'now’) – strftime(‘%s’,’2004-01-01 02:34:56′);

Compute the date of the first Tuesday in October for the current year.

SELECT date(‘now’,'start of year’,'+9 months’,'weekday 2′);

Compute the time since the unix epoch in seconds (like strftime(‘%s’,'now’) except includes fractional part):

SELECT (julianday(‘now’) – 2440587.5)*86400.0;