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SQL: Implement TO_CHAR() function (#66486)

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SQL: Implement the TO_CHAR() function

* The implementation is according to PostgreSQL 13 specs:
https://www.postgresql.org/docs/13/functions-formatting.html
* Tested against actual output from PostgreSQL 13 using randomized inputs
* All the Postgres formats are supported, there is also partial supports
 for the modifiers (`FM` and `TH` are supported)
* Random unit test data generator script in case we need to upgrade the
 formatter in the future
* Documentation
* Integration tests

Co-authored-by: Michał Wąsowicz <mwasowicz7@gmail.com>
Co-authored-by: Andras Palinkas <andras.palinkas@elastic.co>
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Andras Palinkas 2021-01-20 18:32:10 -05:00 • committed by GitHub
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60
docs/reference/sql/functions/date-time.asciidoc
View file

@ -791,15 +791,12 @@ If any of the two arguments is `null` or the pattern is an empty string `null` i
[NOTE]
If the 1st argument is of type `time`, then pattern specified by the 2nd argument cannot contain date related units
(e.g. 'dd', 'MM', 'YYYY', etc.). If it contains such units an error is returned.
*Special Cases*
- Format specifier `F` will be working similar to format specifier `f`.
(e.g. 'dd', 'MM', 'YYYY', etc.). If it contains such units an error is returned. +
Format specifier `F` will be working similar to format specifier `f`.
It will return the fractional part of seconds, and the number of digits will be same as of the number of `Fs` provided as input (up to 9 digits).
Result will contain `0` appended in the end to match with number of `F` provided.
e.g.: for a time part `10:20:30.1234` and pattern `HH:mm:ss.FFFFFF`, the output string of the function would be: `10:20:30.123400`.
- Format Specifier `y` will return year-of-era instead of one/two low-order digits.
e.g.: for a time part `10:20:30.1234` and pattern `HH:mm:ss.FFFFFF`, the output string of the function would be: `10:20:30.123400`. +
Format specifier `y` will return year-of-era instead of one/two low-order digits.
eg.: For year `2009`, `y` will be returning `2009` instead of `9`. For year `43`, `y` format specifier will return `43`.
- Special characters like `"` , `\` and `%` will be returned as it is without any change. eg.: formatting date `17-sep-2020` with `%M` will return `%9`
@ -818,6 +815,55 @@ include-tagged::{sql-specs}/docs/docs.csv-spec[formatDateTime]
include-tagged::{sql-specs}/docs/docs.csv-spec[formatTime]
--------------------------------------------------
[[sql-functions-datetime-to_char]]
==== `TO_CHAR`
.Synopsis:
[source, sql]
--------------------------------------------------
TO_CHAR(
date_exp/datetime_exp/time_exp, <1>
string_exp) <2>
--------------------------------------------------
*Input*:
<1> date/datetime/time expression
<2> format pattern
*Output*: string
*Description*: Returns the date/datetime/time as a string using the format specified in the 2nd argument. The formatting
pattern conforms to
https://www.postgresql.org/docs/13/functions-formatting.html[PostgreSQL Template Patterns for Date/Time Formatting].
If any of the two arguments is `null` or the pattern is an empty string `null` is returned.
[NOTE]
If the 1st argument is of type `time`, then the pattern specified by the 2nd argument cannot contain date related units
(e.g. 'dd', 'MM', 'YYYY', etc.). If it contains such units an error is returned. +
The result of the patterns `TZ` and `tz` (time zone abbreviations) in some cases differ from the results returned by the `TO_CHAR`
in PostgreSQL. The reason is that the time zone abbreviations specified by the JDK are different from the ones specified by PostgreSQL.
This function might show an actual time zone abbreviation instead of the generic `LMT` or empty string or offset returned by the PostgreSQL
implementation. The summer/daylight markers might also differ between the two implementations (e.g. will show `HT` instead of `HST`
for Hawaii). +
The `FX`, `TM`, `SP` pattern modifiers are not supported and will show up as `FX`, `TM`, `SP` literals in the output.
[source, sql]
--------------------------------------------------
include-tagged::{sql-specs}/docs/docs.csv-spec[toCharDate]
--------------------------------------------------
[source, sql]
--------------------------------------------------
include-tagged::{sql-specs}/docs/docs.csv-spec[toCharDateTime]
--------------------------------------------------
[source, sql]
--------------------------------------------------
include-tagged::{sql-specs}/docs/docs.csv-spec[toCharTime]
--------------------------------------------------
[[sql-functions-datetime-day]]
==== `DAY_OF_MONTH/DOM/DAY`

5
docs/reference/sql/functions/index.asciidoc
View file

@ -59,13 +59,13 @@
** <<sql-functions-datetime-datetimeformat>>
** <<sql-functions-datetime-datetimeparse>>
** <<sql-functions-datetime-format>>
** <<sql-functions-datetime-timeparse>>
** <<sql-functions-datetime-part>>
** <<sql-functions-datetime-trunc>>
** <<sql-functions-datetime-day>>
** <<sql-functions-datetime-dow>>
** <<sql-functions-datetime-doy>>
** <<sql-functions-datetime-dayname>>
** <<sql-functions-datetime-extract>>
** <<sql-functions-datetime-hour>>
** <<sql-functions-datetime-isodow>>
** <<sql-functions-datetime-isoweek>>
@ -76,10 +76,11 @@
** <<sql-functions-now>>
** <<sql-functions-datetime-second>>
** <<sql-functions-datetime-quarter>>
** <<sql-functions-datetime-timeparse>>
** <<sql-functions-datetime-to_char>>
** <<sql-functions-today>>
** <<sql-functions-datetime-week>>
** <<sql-functions-datetime-year>>
** <<sql-functions-datetime-extract>>
* <<sql-functions-search>>
** <<sql-functions-search-match>>
** <<sql-functions-search-query>>