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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

FunctionReturn TypeDescriptionExample
to_char(timestamp, text)textconvert time stamp to stringto_char(current_timestamp, 'HH12:MI:SS')
to_char(interval, text)textconvert interval to stringto_char(interval '15h 2m 12s', 'HH24:MI:SS')
to_char(int, text)textconvert integer to stringto_char(125, '999')
to_char(double precision, text)textconvert real/double precision to stringto_char(125.8::real, '999D9')
to_char(numeric, text)textconvert numeric to stringto_char(-125.8, '999D99S')
to_date(text, text)dateconvert string to dateto_date('05 Dec 2000', 'DD Mon YYYY')
to_number(text, text)numericconvert string to numericto_number('12,454.8-', '99G999D9S')
to_timestamp(text, text)timestamp with time zoneconvert string to time stampto_timestamp('05 Dec 2000', 'DD Mon YYYY')
to_timestamp(double precision)timestamp with time zoneconvert Unix epoch to time stampto_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

PatternDescription
HHhour of day (01-12)
HH12hour of day (01-12)
HH24hour of day (00-23)
MIminute (00-59)
SSsecond (00-59)
MSmillisecond (000-999)
USmicrosecond (000000-999999)
SSSSseconds past midnight (0-86399)
AM, am, PM or pmmeridiem indicator (without periods)
A.M., a.m., P.M. or p.m.meridiem indicator (with periods)
Y,YYYyear (4 and more digits) with comma
YYYYyear (4 and more digits)
YYYlast 3 digits of year
YYlast 2 digits of year
Ylast digit of year
IYYYISO year (4 and more digits)
IYYlast 3 digits of ISO year
IYlast 2 digits of ISO year
Ilast digit of ISO year
BC, bc, AD or adera indicator (without periods)
B.C., b.c., A.D. or a.d.era indicator (with periods)
MONTHfull uppercase month name (blank-padded to 9 chars)
Monthfull capitalized month name (blank-padded to 9 chars)
monthfull lowercase month name (blank-padded to 9 chars)
MONabbreviated uppercase month name (3 chars in English, localized lengths vary)
Monabbreviated capitalized month name (3 chars in English, localized lengths vary)
monabbreviated lowercase month name (3 chars in English, localized lengths vary)
MMmonth number (01-12)
DAYfull uppercase day name (blank-padded to 9 chars)
Dayfull capitalized day name (blank-padded to 9 chars)
dayfull lowercase day name (blank-padded to 9 chars)
DYabbreviated uppercase day name (3 chars in English, localized lengths vary)
Dyabbreviated capitalized day name (3 chars in English, localized lengths vary)
dyabbreviated lowercase day name (3 chars in English, localized lengths vary)
DDDday of year (001-366)
IDDDISO day of year (001-371; day 1 of the year is Monday of the first ISO week.)
DDday of month (01-31)
Dday of the week, Sunday(1) to Saturday(7)
IDISO day of the week, Monday(1) to Sunday(7)
Wweek of month (1-5) (The first week starts on the first day of the month.)
WWweek number of year (1-53) (The first week starts on the first day of the year.)
IWISO week number of year (01 - 53; the first Thursday of the new year is in week 1.)
CCcentury (2 digits) (The twenty-first century starts on 2001-01-01.)
JJulian Day (days since November 24, 4714 BC at midnight)
Qquarter
RMmonth in uppercase Roman numerals (I-XII; I=January)
rmmonth in lowercase Roman numerals (i-xii; i=January)
TZuppercase time-zone name
tzlowercase 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

ModifierDescriptionExample
FM prefixfill mode (suppress padding blanks and zeroes)FMMonth
TH suffixuppercase ordinal number suffixDDTH, e.g., 12TH
th suffixlowercase ordinal number suffixDDth, e.g., 12th
FX prefixfixed format global option (see usage notes)FX Month DD Day
TM prefixtranslation mode (print localized day and month names based on lc_time)TMMonth
SP suffixspell 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', ...) function, but to_char(..., 'D')'s does not match extract('dow', ...)'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

PatternDescription
9value with the specified number of digits
0value with leading zeros
. (period)decimal point
, (comma)group (thousand) separator
PRnegative value in angle brackets
Ssign anchored to number (uses locale)
Lcurrency symbol (uses locale)
Ddecimal point (uses locale)
Ggroup separator (uses locale)
MIminus sign in specified position (if number < 0)
PLplus sign in specified position (if number > 0)
SGplus/minus sign in specified position
RNRoman numeral (input between 1 and 3999)
TH or thordinal number suffix
Vshift specified number of digits (see notes)
EEEEscientific 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

ModifierDescriptionExample
FM prefixfill mode (suppress padding blanks and zeroes)FM9999
TH suffixuppercase ordinal number suffix999TH
th suffixlowercase ordinal number suffix999th

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

Table 9-25. to_char Examples

ExpressionResult
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'
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