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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.

The to_timestamp function can also take a single double precision argument to convert from Unix epoch to timestamp with time zone. (Integer Unix epochs are implicitly cast to double precision.)

Table 9-20. 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_timestamp(text, text) timestamp with time zone convert string to time stamp to_timestamp('05 Dec 2000', 'DD Mon YYYY')
to_timestamp(double precision) timestamp with time zone convert UNIX epoch to time stamp to_timestamp(200120400)
to_number(text, text) numeric convert string to numeric to_number('12,454.8-', '99G999D9S')

In an output template string (for to_char), there are certain patterns that are recognized and replaced with appropriately-formatted data from the value to be formatted. Any text that is not a template pattern is simply copied verbatim. Similarly, in an input template string (for anything but to_char), template patterns identify the parts of the input data string to be looked at and the values to be found there.

Table 9-21 shows the template patterns available for formatting date and time values.

Table 9-21. 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 or A.M. or PM or P.M. meridian indicator (uppercase)
am or a.m. or pm or p.m. meridian indicator (lowercase)
Y,YYY year (4 and more digits) with comma
YYYY year (4 and more digits)
YYY last 3 digits of year
YY last 2 digits of year
Y last digit of year
IYYY ISO year (4 and more digits)
IYY last 3 digits of ISO year
IY last 2 digits of ISO year
I last digits of ISO year
BC or B.C. or AD or A.D. era indicator (uppercase)
bc or b.c. or ad or a.d. era indicator (lowercase)
MONTH full uppercase month name (blank-padded to 9 chars)
Month full mixed-case month name (blank-padded to 9 chars)
month full lowercase month name (blank-padded to 9 chars)
MON abbreviated uppercase month name (3 chars)
Mon abbreviated mixed-case month name (3 chars)
mon abbreviated lowercase month name (3 chars)
MM month number (01-12)
DAY full uppercase day name (blank-padded to 9 chars)
Day full mixed-case day name (blank-padded to 9 chars)
day full lowercase day name (blank-padded to 9 chars)
DY abbreviated uppercase day name (3 chars)
Dy abbreviated mixed-case day name (3 chars)
dy abbreviated lowercase day name (3 chars)
DDD day of year (001-366)
DD day of month (01-31)
D day of week (1-7; Sunday is 1)
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 ISO week number of year (The first Thursday of the new year is in week 1.)
CC century (2 digits)
J Julian Day (days since January 1, 4712 BC)
Q quarter
RM month in Roman numerals (I-XII; I=January) (uppercase)
rm month in Roman numerals (i-xii; i=January) (lowercase)
TZ time-zone name (uppercase)
tz time-zone name (lowercase)

Certain modifiers may 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

Modifier Description Example
FM prefix fill mode (suppress padding blanks and zeroes) FMMonth
TH suffix uppercase ordinal number suffix DDTH
th suffix lowercase ordinal number suffix DDth
FX prefix fixed format global option (see usage notes) FX Month DD Day
SP suffix spell mode (not yet 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.

  • to_timestamp and to_date skip multiple blank spaces in the input string if the FX option is not used. FX must be specified as the first item in the template. For example to_timestamp('2000    JUN', 'YYYY MON') is correct, but to_timestamp('2000    JUN', 'FXYYYY MON') returns an error, because to_timestamp expects one space only.

  • 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 '\\"YYYY Month\\"'. (Two backslashes are necessary because the backslash already has a special meaning in a string constant.)

  • The YYYY conversion from string to timestamp or date has a restriction if you use a year 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 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.

  • Millisecond (MS) and microsecond (US) values in a conversion from string to timestamp are used as part of the seconds 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's day of the week numbering (see the 'D' formatting pattern) is different from that of the extract function.

  • 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

Pattern Description
9 value with the specified number of digits
0 value with leading zeros
. (period) decimal point
, (comma) group (thousand) 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 scientific notation (not implemented yet)

Usage notes for numeric formatting:

  • A sign formatted using SG, PL, or MI is not anchored to the number; for example, to_char(-12, 'S9999') produces '  -12', but to_char(-12, 'MI9999') produces '-  12'. The Oracle implementation does not allow the use of MI ahead of 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.)

Table 9-24 shows some examples of the use of the to_char function.

Table 9-24. 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, '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'

  Published courtesy of The PostgreSQL Global Development Group Design by Interspire