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9.8. Data Type Formatting Functions

The PostgreSQL formatting functions provide a powerful set of tools for converting various data types (date/time, integer, floating point, numeric) to formatted strings and for converting from formatted strings to specific data types. Table 9-20 lists them. These functions all follow a common calling convention: the first argument is the value to be formatted and the second argument is a template that defines the output or input format.

A single-argument to_timestamp function is also available; it accepts a double precision argument and converts from Unix epoch (seconds since 1970-01-01 00:00:00+00) to timestamp with time zone. (Integer Unix epochs are implicitly cast to double precision.)

Table 9-20. Formatting Functions

Function Return Type Description Example
to_char(timestamp, text) text convert time stamp to string to_char(current_timestamp, 'HH12:MI:SS')
to_char(interval, text) text convert interval to string to_char(interval '15h 2m 12s', 'HH24:MI:SS')
to_char(int, text) text convert integer to string to_char(125, '999')
to_char(double precision, text) text convert real/double precision to string to_char(125.8::real, '999D9')
to_char(numeric, text) text convert numeric to string to_char(-125.8, '999D99S')
to_date(text, text) date convert string to date to_date('05 Dec 2000', 'DD Mon YYYY')
to_number(text, text) numeric convert string to numeric to_number('12,454.8-', '99G999D9S')
to_timestamp(text, text) timestamp with time zone convert string to time stamp to_timestamp('05 Dec 2000', 'DD Mon YYYY')
to_timestamp(double precision) timestamp with time zone convert Unix epoch to time stamp to_timestamp(1284352323)

In a to_char output template string, there are certain patterns that are recognized and replaced with appropriately-formatted data based on the given value. Any text that is not a template pattern is simply copied verbatim. Similarly, in an input template string (for the other functions), template patterns identify the values to be supplied by the input data string.

Table 9-21 shows the template patterns available for formatting date and time values.

Table 9-21. Template Patterns for Date/Time Formatting

Pattern Description
HH hour of day (01-12)
HH12 hour of day (01-12)
HH24 hour of day (00-23)
MI minute (00-59)
SS second (00-59)
MS millisecond (000-999)
US microsecond (000000-999999)
SSSS seconds past midnight (0-86399)
AM, am, PM or pm meridiem indicator (without periods)
A.M., a.m., P.M. or p.m. meridiem indicator (with periods)
Y,YYY year (4 and more digits) with comma
YYYY year (4 and more digits)
YYY last 3 digits of year
YY last 2 digits of year
Y last digit of year
IYYY ISO year (4 and more digits)
IYY last 3 digits of ISO year
IY last 2 digits of ISO year
I last digit of ISO year
BC, bc, AD or ad era indicator (without periods)
B.C., b.c., A.D. or a.d. era indicator (with periods)
MONTH full uppercase month name (blank-padded to 9 chars)
Month full capitalized month name (blank-padded to 9 chars)
month full lowercase month name (blank-padded to 9 chars)
MON abbreviated uppercase month name (3 chars in English, localized lengths vary)
Mon abbreviated capitalized month name (3 chars in English, localized lengths vary)
mon abbreviated lowercase month name (3 chars in English, localized lengths vary)
MM month number (01-12)
DAY full uppercase day name (blank-padded to 9 chars)
Day full capitalized day name (blank-padded to 9 chars)
day full lowercase day name (blank-padded to 9 chars)
DY abbreviated uppercase day name (3 chars in English, localized lengths vary)
Dy abbreviated capitalized day name (3 chars in English, localized lengths vary)
dy abbreviated lowercase day name (3 chars in English, localized lengths vary)
DDD day of year (001-366)
IDDD ISO day of year (001-371; day 1 of the year is Monday of the first ISO week.)
DD day of month (01-31)
D day of the week, Sunday(1) to Saturday(7)
ID ISO day of the week, Monday(1) to Sunday(7)
W week of month (1-5) (The first week starts on the first day of the month.)
WW week number of year (1-53) (The first week starts on the first day of the year.)
IW ISO week number of year (01 - 53; the first Thursday of the new year is in week 1.)
CC century (2 digits) (The twenty-first century starts on 2001-01-01.)
J Julian Day (days since November 24, 4714 BC at midnight)
Q quarter
RM month in uppercase Roman numerals (I-XII; I=January)
rm month in lowercase Roman numerals (i-xii; i=January)
TZ uppercase time-zone name
tz lowercase time-zone name

Modifiers can be applied to any template pattern to alter its behavior. For example, FMMonth is the Month pattern with the FM modifier. Table 9-22 shows the modifier patterns for date/time formatting.

Table 9-22. Template Pattern Modifiers for Date/Time Formatting

Modifier Description Example
FM prefix fill mode (suppress padding blanks and zeroes) FMMonth
TH suffix uppercase ordinal number suffix DDTH, e.g., 12TH
th suffix lowercase ordinal number suffix DDth, e.g., 12th
FX prefix fixed format global option (see usage notes) FX Month DD Day
TM prefix translation mode (print localized day and month names based on lc_time) TMMonth
SP suffix spell mode (not implemented) DDSP

Usage notes for date/time formatting:

  • FM suppresses leading zeroes and trailing blanks that would otherwise be added to make the output of a pattern be fixed-width.

  • TM does not include trailing blanks.

  • to_timestamp and to_date skip multiple blank spaces in the input string unless the FX option is used. For example, to_timestamp('2000    JUN', 'YYYY MON') works, but to_timestamp('2000    JUN', 'FXYYYY MON') returns an error because to_timestamp expects one space only. FX must be specified as the first item in the template.

  • Ordinary text is allowed in to_char templates and will be output literally. You can put a substring in double quotes to force it to be interpreted as literal text even if it contains pattern key words. For example, in '"Hello Year "YYYY', the YYYY will be replaced by the year data, but the single Y in Year will not be.

  • If you want to have a double quote in the output you must precede it with a backslash, for example E'\\"YYYY Month\\"'. (Two backslashes are necessary because the backslash has special meaning when using the escape string syntax.)

  • The YYYY conversion from string to timestamp or date has a restriction when processing years with more than 4 digits. You must use some non-digit character or template after YYYY, otherwise the year is always interpreted as 4 digits. For example (with the year 20000): to_date('200001131', 'YYYYMMDD') will be interpreted as a 4-digit year; instead use a non-digit separator after the year, like to_date('20000-1131', 'YYYY-MMDD') or to_date('20000Nov31', 'YYYYMonDD').

  • In conversions from string to timestamp or date, the CC (century) field is ignored if there is a YYY, YYYY or Y,YYY field. If CC is used with YY or Y then the year is computed as (CC-1)*100+YY.

  • An ISO week date (as distinct from a Gregorian date) can be specified to to_timestamp and to_date in one of two ways:

    • Year, week, and weekday: for example to_date('2006-42-4', 'IYYY-IW-ID') returns the date 2006-10-19. If you omit the weekday it is assumed to be 1 (Monday).

    • Year and day of year: for example to_date('2006-291', 'IYYY-IDDD') also returns 2006-10-19.

    Attempting to construct a date using a mixture of ISO week and Gregorian date fields is nonsensical, and will cause an error. In the context of an ISO year, the concept of a "month" or "day of month" has no meaning. In the context of a Gregorian year, the ISO week has no meaning. Users should avoid mixing Gregorian and ISO date specifications.

  • In a conversion from string to timestamp, millisecond (MS) or microsecond (US) values are used as the seconds digits after the decimal point. For example to_timestamp('12:3', 'SS:MS') is not 3 milliseconds, but 300, because the conversion counts it as 12 + 0.3 seconds. This means for the format SS:MS, the input values 12:3, 12:30, and 12:300 specify the same number of milliseconds. To get three milliseconds, one must use 12:003, which the conversion counts as 12 + 0.003 = 12.003 seconds.

    Here is a more complex example: to_timestamp('15:12:02.020.001230', 'HH:MI:SS.MS.US') is 15 hours, 12 minutes, and 2 seconds + 20 milliseconds + 1230 microseconds = 2.021230 seconds.

  • to_char(..., 'ID')'s day of the week numbering matches the extract(isodow from ...) function, but to_char(..., 'D')'s does not match extract(dow from ...)'s day numbering.

  • to_char(interval) formats HH and HH12 as hours in a single day, while HH24 can output hours exceeding a single day, e.g., >24.

Table 9-23 shows the template patterns available for formatting numeric values.

Table 9-23. Template Patterns for Numeric Formatting

Pattern Description
9 value with the specified number of digits
0 value with leading zeros
. (period) decimal point
, (comma) group (thousand) separator
PR negative value in angle brackets
S sign anchored to number (uses locale)
L currency symbol (uses locale)
D decimal point (uses locale)
G group separator (uses locale)
MI minus sign in specified position (if number < 0)
PL plus sign in specified position (if number > 0)
SG plus/minus sign in specified position
RN Roman numeral (input between 1 and 3999)
TH or th ordinal number suffix
V shift specified number of digits (see notes)
EEEE scientific notation (not implemented)

Usage notes for numeric formatting:

  • A sign formatted using SG, PL, or MI is not anchored to the number; for example, to_char(-12, 'MI9999') produces '-  12' but to_char(-12, 'S9999') produces '  -12'. The Oracle implementation does not allow the use of MI before 9, but rather requires that 9 precede MI.

  • 9 results in a value with the same number of digits as there are 9s. If a digit is not available it outputs a space.

  • TH does not convert values less than zero and does not convert fractional numbers.

  • PL, SG, and TH are PostgreSQL extensions.

  • V effectively multiplies the input values by 10^n, where n is the number of digits following V. to_char does not support the use of V combined with a decimal point (e.g., 99.9V99 is not allowed).

Certain modifiers can be applied to any template pattern to alter its behavior. For example, FM9999 is the 9999 pattern with the FM modifier. Table 9-24 shows the modifier patterns for numeric formatting.

Table 9-24. Template Pattern Modifiers for Numeric Formatting

Modifier Description Example
FM prefix fill mode (suppress padding blanks and zeroes) FM9999
TH suffix uppercase ordinal number suffix 999TH
th suffix lowercase ordinal number suffix 999th

Table 9-25 shows some examples of the use of the to_char function.

Table 9-25. to_char Examples

Expression Result
to_char(current_timestamp, 'Day, DD  HH12:MI:SS') 'Tuesday  , 06  05:39:18'
to_char(current_timestamp, 'FMDay, FMDD  HH12:MI:SS') 'Tuesday, 6  05:39:18'
to_char(-0.1, '99.99') '  -.10'
to_char(-0.1, 'FM9.99') '-.1'
to_char(0.1, '0.9') ' 0.1'
to_char(12, '9990999.9') '    0012.0'
to_char(12, 'FM9990999.9') '0012.'
to_char(485, '999') ' 485'
to_char(-485, '999') '-485'
to_char(485, '9 9 9') ' 4 8 5'
to_char(1485, '9,999') ' 1,485'
to_char(1485, '9G999') ' 1 485'
to_char(148.5, '999.999') ' 148.500'
to_char(148.5, 'FM999.999') '148.5'
to_char(148.5, 'FM999.990') '148.500'
to_char(148.5, '999D999') ' 148,500'
to_char(3148.5, '9G999D999') ' 3 148,500'
to_char(-485, '999S') '485-'
to_char(-485, '999MI') '485-'
to_char(485, '999MI') '485 '
to_char(485, 'FM999MI') '485'
to_char(485, 'PL999') '+485'
to_char(485, 'SG999') '+485'
to_char(-485, 'SG999') '-485'
to_char(-485, '9SG99') '4-85'
to_char(-485, '999PR') '<485>'
to_char(485, 'L999') 'DM 485
to_char(485, 'RN') '        CDLXXXV'
to_char(485, 'FMRN') 'CDLXXXV'
to_char(5.2, 'FMRN') 'V'
to_char(482, '999th') ' 482nd'
to_char(485, '"Good number:"999') 'Good number: 485'
to_char(485.8, '"Pre:"999" Post:" .999') 'Pre: 485 Post: .800'
to_char(12, '99V999') ' 12000'
to_char(12.4, '99V999') ' 12400'
to_char(12.45, '99V9') ' 125'

Comments


Sept. 12, 2009, 7:41 a.m.

to_char(interval '0d 0h 12m 44s', 'DD HH MI SS');
with HH and HH12 will return 12 instead of 0.

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