Postgres-XC 1.1 Documentation
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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.

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 9-20. 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_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')`
``to_timestamp(`double precision`)`` | `timestamp with time zone` | convert Unix epoch to time stamp | `to_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 9-21 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`, `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 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 digit of ISO 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` | ISO day of 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 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` | ISO week number of year (01 - 53; the first Thursday of the new year is in week 1.)
`CC` | century (2 digits) (The twenty-first century starts on 2001-01-01.)
`J` | Julian Day (days since November 24, 4714 BC at midnight)
`Q` | quarter (ignored by `to_date` and `to_timestamp`)
`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 name
`tz` | lower case time-zone name

Modifiers can be applied to any template pattern to alter its behavior. For example, `FMMonth` is the `Month` pattern with the `FM` modifier. Table 9-22 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 trailing zeroes) | `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` 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\"'`.

- 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 `(CC-1)*100+YY`.

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

  - Year, week, 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 construct a date using a mixture of ISO week and Gregorian date fields is nonsensical, and will cause an error. In the context of an ISO 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. Users should avoid mixing Gregorian and ISO date specifications.

- 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', 'HH: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 9-23 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` | exponent for scientific notation

Usage notes for numeric formatting:

- 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`.

- `9` results in a value with the same number of digits as there are `9`s. 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).

- `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, `FM9999` is the `9999` pattern with the `FM` modifier. Table 9-24 shows the modifier patterns for numeric formatting.

Table 9-24. Template Pattern Modifiers for Numeric Formatting

Modifier | Description | Example
--- | --- | ---
`FM` prefix | fill mode (suppress padding blanks and trailing zeroes) | `FM9999`
`TH` suffix | upper case ordinal number suffix | `999TH`
`th` suffix | lower case ordinal number suffix | `999th`

Table 9-25 shows some examples of the use of the `to_char` function.

Table 9-25. `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'`
`to_char(0.0004859, '9.99EEEE')` | `' 4.86e-04'`

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