2.6. Data Type Formatting Functions

The Hyper formatting functions provide a powerful set of tools for converting various data types to formatted strings and for converting from formatted strings to specific data types. Table 2.13 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 2.13. Formatting Functions

FunctionReturn TypeDescriptionExample
to_char(timestamp, text) textconvert timestamp 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_date(text, text) dateconvert string to dateto_date('05 Dec 2000', 'DD Mon YYYY')
to_timestamp(text, text) timestamp with time zoneconvert string to timestampto_timestamp('05 Dec 2000', 'DD Mon YYYY')

Note

There is also a single-argument to_timestamp function; see Table 2.18.

Tip

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.

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. If there are characters in the template string that are not template patterns, the corresponding characters in the input data string are simply skipped over (whether or not they are equal to the template string characters).

Table 2.14 shows the template patterns available for formatting date and time values.

Table 2.14. 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 English month name (blank-padded to 9 chars)
Monthfull capitalized English month name (blank-padded to 9 chars)
monthfull lower case English month name (blank-padded to 9 chars)
MONabbreviated upper case English month name (3 chars)
Monabbreviated capitalized English month name (3 chars)
monabbreviated lower case English month name (3 chars)
MMmonth number (01-12)
DAYfull upper case English day name (blank-padded to 9 chars)
Dayfull capitalized English day name (blank-padded to 9 chars)
dayfull lower case English day name (blank-padded to 9 chars)
DYabbreviated upper case English day name (3 chars)
Dyabbreviated capitalized English day name (3 chars)
dyabbreviated lower case English day name (3 chars)
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
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)
TZHtime-zone hours
TZMtime-zone minutes
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 2.15 shows the modifier patterns for date/time formatting.

Table 2.15. 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

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 Hyper, as well as in PostgreSQL, FM modifies only the next specification, while in other database systems FM might affect all subsequent specifications, and repeated FM modifiers toggle fill mode on and off.

  • 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 template patterns. 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_timestamp and to_date, literal text and double-quoted strings result in skipping the number of characters contained in the string; for example "XX" skips two input characters (whether or not they are XX).

  • If you want to have a double quote in the output you must precede it with a backslash, for example '\"YYYY Month\"'. Backslashes are not otherwise special outside of double-quoted strings. Within a double-quoted string, a backslash causes the next character to be taken literally, whatever it is (but this has no special effect unless the next character is a double quote or another backslash).

  • 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, 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 contradictory and will thus 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. On the other hand, in the context of a Gregorian year, the ISO week has no meaning.

    Caution

    While to_date and to_timestamp 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.

  • 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 2.16 shows some examples of the use of the to_char function.

Table 2.16. 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'