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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 9.23 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

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')

 
+

Note

There is also a single-argument to_timestamp function; see Table 9.30.

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. 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, PM or pm

meridiem indicator (without periods)

A.M., a.m., P.M. or p.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, AD or ad

era indicator (without periods)

B.C., b.c., A.D. or a.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

FM prefix

fill mode (suppress leading zeroes and padding blanks)

FMMonth

TH suffix

upper case ordinal number suffix

DDTH, e.g., 12TH

th suffix

lower case 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. 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 “[.quote]#month”# or “[.quote]#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 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)

TH or th

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^`n, where n 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

FM prefix

fill mode (suppress trailing zeroes and padding blanks)

FM99.99

TH suffix

upper case ordinal number suffix

999TH

th suffix

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'

 
+
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