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 9.23 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.
Table 9.23. Formatting Functions
     There is also a single-argument to_timestamp
     function; see Table 9.30.
    
     to_timestamp and to_date
     exist to handle input formats that cannot be converted by
     simple casting.  For most standard date/time formats, simply casting the
     source string to the required data type works, and is much easier.
     Similarly, to_number is unnecessary for standard numeric
     representations.
    
    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 9.24 shows the template patterns available for formatting date and time values.
Table 9.24. 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,PMorpm | meridiem indicator (without periods) | 
| A.M.,a.m.,P.M.orp.m. | meridiem indicator (with periods) | 
| Y,YYY | year (4 or more digits) with comma | 
| YYYY | year (4 or more digits) | 
| YYY | last 3 digits of year | 
| YY | last 2 digits of year | 
| Y | last digit of year | 
| IYYY | ISO 8601 week-numbering year (4 or more digits) | 
| IYY | last 3 digits of ISO 8601 week-numbering year | 
| IY | last 2 digits of ISO 8601 week-numbering year | 
| I | last digit of ISO 8601 week-numbering year | 
| BC,bc,ADorad | era indicator (without periods) | 
| B.C.,b.c.,A.D.ora.d. | era indicator (with periods) | 
| MONTH | full upper case month name (blank-padded to 9 chars) | 
| Month | full capitalized month name (blank-padded to 9 chars) | 
| month | full lower case month name (blank-padded to 9 chars) | 
| MON | abbreviated upper case month name (3 chars in English, localized lengths vary) | 
| Mon | abbreviated capitalized month name (3 chars in English, localized lengths vary) | 
| mon | abbreviated lower case month name (3 chars in English, localized lengths vary) | 
| MM | month number (01-12) | 
| DAY | full upper case day name (blank-padded to 9 chars) | 
| Day | full capitalized day name (blank-padded to 9 chars) | 
| day | full lower case day name (blank-padded to 9 chars) | 
| DY | abbreviated upper case day name (3 chars in English, localized lengths vary) | 
| Dy | abbreviated capitalized day name (3 chars in English, localized lengths vary) | 
| dy | abbreviated lower case day name (3 chars in English, localized lengths vary) | 
| DDD | day of year (001-366) | 
| IDDD | day of ISO 8601 week-numbering 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 8601 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 | week number of ISO 8601 week-numbering year (01-53; the first Thursday of the year is in week 1) | 
| CC | century (2 digits) (the twenty-first century starts on 2001-01-01) | 
| J | Julian Date (integer days since November 24, 4714 BC at local midnight; see Section B.7) | 
| Q | quarter | 
| RM | month in upper case Roman numerals (I-XII; I=January) | 
| rm | month in lower case Roman numerals (i-xii; i=January) | 
| TZ | upper case time-zone abbreviation
         (only supported in to_char) | 
| tz | lower case time-zone abbreviation
         (only supported in to_char) | 
| OF | time-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 9.25 shows the
    modifier patterns for date/time formatting.
   
Table 9.25. Template Pattern Modifiers for Date/Time Formatting
| Modifier | Description | Example | 
|---|---|---|
| FMprefix | fill mode (suppress leading zeroes and padding blanks) | FMMonth | 
| THsuffix | upper case ordinal number suffix | DDTH, e.g.,12TH | 
| thsuffix | lower case ordinal number suffix | DDth, e.g.,12th | 
| FXprefix | fixed format global option (see usage notes) | FX Month DD Day | 
| TMprefix | translation mode (print localized day and month names based on lc_time) | TMMonth | 
| SPsuffix | 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.  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.
      
       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\"'. 
      
       In to_timestamp and to_date,
       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.
      
       In to_timestamp and to_date,
       negative years are treated as signifying BC.  If you write both a
       negative year and an explicit BC field, you get AD
       again.  An input of year zero is treated as 1 BC.
      
       In to_timestamp and to_date,
       the YYYY conversion 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 to_timestamp and to_date,
       the CC (century) field is accepted but ignored
       if there is a YYY, YYYY or
       Y,YYY field. If CC is used with
       YY or Y then the result is
       computed as that year in the specified century.  If the century is
       specified but the year is not, the first year of the century
       is assumed.
      
       In to_timestamp and to_date,
       weekday names or numbers (DAY, D,
       and related field types) are accepted but are ignored for purposes of
       computing the result.  The same is true for quarter
       (Q) fields.
      
       In to_timestamp and to_date,
       an ISO 8601 week-numbering date (as distinct from a Gregorian date)
       can be specified 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.
        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 to_timestamp, millisecond
       (MS) or microsecond (US)
       fields 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 treats it as 12 + 0.3 seconds.
       So, 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 write
       12.003, which the conversion treats 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, for example zero hours
        and 36 hours both output as 12, while HH24
        outputs the full hour value, which can exceed 23 in
        an interval value.
      
Table 9.26 shows the template patterns available for formatting numeric values.
Table 9.26. Template Patterns for Numeric Formatting
| Pattern | Description | 
|---|---|
| 9 | digit position (can be dropped if insignificant) | 
| 0 | digit position (will not be dropped, even if insignificant) | 
| .(period) | decimal point | 
| ,(comma) | group (thousands) 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) | 
| THorth | ordinal number suffix | 
| V | shift specified number of digits (see notes) | 
| EEEE | exponent 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 with to_char
       multiplies the input values by
       10^, where
       nn is the number of digits following
       V.  V with
       to_number divides in a similar manner.
       to_char and to_number
       do 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 9.27 shows the
    modifier patterns for numeric formatting.
   
Table 9.27. Template Pattern Modifiers for Numeric Formatting
| Modifier | Description | Example | 
|---|---|---|
| FMprefix | fill mode (suppress trailing zeroes and padding blanks) | FM99.99 | 
| THsuffix | upper case ordinal number suffix | 999TH | 
| thsuffix | lower case ordinal number suffix | 999th | 
   Table 9.28 shows some
   examples of the use of the to_char function.
  
Table 9.28. 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, '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' |