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 9.21 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 9.21. 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 9.22 shows the template patterns available for formatting date and time values.

Table 9.22. 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 or more digits) with comma
YYYYyear (4 or more digits)
YYYlast 3 digits of year
YYlast 2 digits of year
Ylast digit of year
IYYYISO 8601 week-numbering year (4 or more digits)
IYYlast 3 digits of ISO 8601 week-numbering year
IYlast 2 digits of ISO 8601 week-numbering year
Ilast digit of ISO 8601 week-numbering year
BC, bc, AD or adera indicator (without periods)
B.C., b.c., A.D. or a.d.era indicator (with periods)
MONTHfull upper case month name (blank-padded to 9 chars)
Monthfull capitalized month name (blank-padded to 9 chars)
monthfull lower case month name (blank-padded to 9 chars)
MONabbreviated upper case month name (3 chars in English, localized lengths vary)
Monabbreviated capitalized month name (3 chars in English, localized lengths vary)
monabbreviated lower case month name (3 chars in English, localized lengths vary)
MMmonth number (01-12)
DAYfull upper case day name (blank-padded to 9 chars)
Dayfull capitalized day name (blank-padded to 9 chars)
dayfull lower case day name (blank-padded to 9 chars)
DYabbreviated upper case day name (3 chars in English, localized lengths vary)
Dyabbreviated capitalized day name (3 chars in English, localized lengths vary)
dyabbreviated lower case day name (3 chars in English, localized lengths vary)
DDDday of year (001-366)
IDDDday of ISO 8601 week-numbering 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 8601 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)
IWweek number of ISO 8601 week-numbering year (01-53; the first Thursday of the year is in week 1)
CCcentury (2 digits) (the twenty-first century starts on 2001-01-01)
JJulian Day (integer days since November 24, 4714 BC at midnight UTC)
Qquarter (ignored by to_date and to_timestamp)
RMmonth in upper case Roman numerals (I-XII; I=January)
rmmonth in lower case Roman numerals (i-xii; i=January)
TZupper case time-zone abbreviation (only supported in to_char)
tzlower case time-zone abbreviation (only supported in to_char)
OFtime-zone offset from UTC (only supported in to_char)

Modifiers can be applied to any template pattern to alter its behavior. For example, FMMonth is the Month pattern with the FM modifier. Table 9.23 shows the modifier patterns for date/time formatting.

Table 9.23. Template Pattern Modifiers for Date/Time Formatting

ModifierDescriptionExample
FM prefixfill mode (suppress leading zeroes and padding blanks)FMMonth
TH suffixupper case ordinal number suffixDDTH, e.g., 12TH
th suffixlower case 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. In PostgreSQL, FM modifies only the next specification, while in Oracle FM affects all subsequent specifications, and repeated FM modifiers toggle fill mode on and off.

  • TM does not include trailing blanks. to_timestamp and to_date ignore the TM modifier.

  • 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.

  • to_timestamp and to_date exist to handle input formats that cannot be converted by simple casting. These functions interpret input liberally, with minimal error checking. While they produce valid output, the conversion can yield unexpected results. For example, input to these functions is not restricted by normal ranges, thus to_date('20096040','YYYYMMDD') returns 2014-01-17 rather than causing an error. Casting does not have this behavior.

  • 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. In to_date, to_number, and to_timestamp, double-quoted strings skip the number of input characters contained in the string, e.g. "XX" skips two input characters.

  • If you want to have a double quote in the output you must precede it with a backslash, for example '\"YYYY Month\"'.

  • If the year format specification is less than four digits, e.g. YYY, and the supplied year is less than four digits, the year will be adjusted to be nearest to the year 2020, e.g. 95 becomes 1995.

  • 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 the year in the specified century. If the century is specified but the year is not, the first year of the century is assumed.

  • An ISO 8601 week-numbering date (as distinct from a Gregorian date) can be specified to to_timestamp and to_date in one of two ways:

    • Year, week number, 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 enter a date using a mixture of ISO 8601 week-numbering fields and Gregorian date fields is nonsensical, and will cause an error. In the context of an ISO 8601 week-numbering 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.

    Caution

    While to_date will reject a mixture of Gregorian and ISO week-numbering date fields, to_char will not, since output format specifications like YYYY-MM-DD (IYYY-IDDD) can be useful. But avoid writing something like IYYY-MM-DD; that would yield surprising results near the start of the year. (See Section 9.9.1 for more information.)

  • 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', 'HH24: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 shown on a 12-hour clock, i.e. zero hours and 36 hours output as 12, while HH24 outputs the full hour value, which can exceed 23 for intervals.

Table 9.24 shows the template patterns available for formatting numeric values.

Table 9.24. Template Patterns for Numeric Formatting

PatternDescription
9digit position (can be dropped if insignificant)
0digit position (will not be dropped, even if insignificant)
. (period)decimal point
, (comma)group (thousands) 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)
EEEEexponent for scientific notation

Usage notes for numeric formatting:

  • 0 specifies a digit position that will always be printed, even if it contains a leading/trailing zero. 9 also specifies a digit position, but if it is a leading zero then it will be replaced by a space, while if it is a trailing zero and fill mode is specified then it will be deleted. (For to_number(), these two pattern characters are equivalent.)

  • The pattern characters S, L, D, and G represent the sign, currency symbol, decimal point, and thousands separator characters defined by the current locale (see lc_monetary and lc_numeric). The pattern characters period and comma represent those exact characters, with the meanings of decimal point and thousands separator, regardless of locale.

  • If no explicit provision is made for a sign in to_char()'s pattern, one column will be reserved for the sign, and it will be anchored to (appear just left of) the number. If S appears just left of some 9's, it will likewise be anchored to the number.

  • 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.)

  • 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).

  • EEEE (scientific notation) cannot be used in combination with any of the other formatting patterns or modifiers other than digit and decimal point patterns, and must be at the end of the format string (e.g., 9.99EEEE is a valid pattern).

Certain modifiers can be applied to any template pattern to alter its behavior. For example, FM99.99 is the 99.99 pattern with the FM modifier. Table 9.25 shows the modifier patterns for numeric formatting.

Table 9.25. Template Pattern Modifiers for Numeric Formatting

ModifierDescriptionExample
FM prefixfill mode (suppress trailing zeroes and padding blanks)FM99.99
TH suffixupper case ordinal number suffix999TH
th suffixlower case ordinal number suffix999th

Table 9.26 shows some examples of the use of the to_char function.

Table 9.26. 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, 'FM90.99')'-0.1'
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'
to_char(0.0004859, '9.99EEEE')' 4.86e-04'