From: akr@...
Date: 2019-07-16T02:17:54+00:00
Subject: [ruby-core:93800] [Ruby master Feature#16005] A variation of Time.iso8601 that can parse yyyy-MM-dd HH:mm:ss

Issue #16005 has been updated by akr (Akira Tanaka).


matsuda (Akira Matsuda) wrote:
> > I would be OK with modifying Time.iso8601 to make either T or space a valid date/time separator.
> 
> In fact this was my first proposal. I firstly asked @akr about that exact modification on `Time.iso8601`, but he didn't like the idea because that behavior is against ISO 8601 specification.

I said its against XML Schema.
https://www.w3.org/TR/xmlschema-2/

Time[.#]iso8601 is alias of Time[.#]xmlschema.

ISO 8601 defines various representation of date and time.
For example, 1985102T1015Z is valid (10:15 of 102th day of 1985 in UTC).
So, practically, some profile (subset) is required.

XML Schema defines a such profile and it defines that [T] is mandatory.

ISO 8601 itself describes that [T] can be omitted by mutual agreement.

But as far as considering XML Schema as a mutual agreement, we cannot omit [T].

Apart from that, I extracted timestamp related syntax from the SQL 92 standard.

```
<timestamp literal> ::=
     TIMESTAMP <timestamp string>

<timestamp string> ::=
     <quote> <date value> <space> <time value> [ <time zone interval> ] <quote>

<date value> ::=
     <years value> <minus sign> <months value> <minus sign> <days value>

<time value> ::=
     <hours value> <colon> <minutes value> <colon> <seconds value>

<time zone interval> ::=
     <sign> <hours value> <colon> <minutes value>

<years value> ::= <datetime value>

<months value> ::= <datetime value>

<days value> ::= <datetime value>

<hours value> ::= <datetime value>

<minutes value> ::= <datetime value>

<seconds value> ::=
       <seconds integer value> [ <period> [ <seconds fraction> ] ]

<seconds integer value> ::= <unsigned integer>

<seconds fraction> ::= <unsigned integer>

<datetime value> ::= <unsigned integer>

<unsigned integer> ::= <digit>...

<sign> ::= <plus sign> | <minus sign>

<digit> ::=
     0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

<space> ::= !! space character in character set in use

<quote> ::= '

<plus sign> ::= + 

<minus sign> ::= -

<period> ::= . 

<colon> ::= :
```

I feel it is difficult to consider ISO 8601 variant because
months value, days value, hours value, minutes value and
seconds integer value can be one digit (and 3 or more digits).

Also, I'm still not certain that what Time object to be generated
when time zone interval is not given.





----------------------------------------
Feature #16005: A variation of Time.iso8601 that can parse yyyy-MM-dd HH:mm:ss
https://bugs.ruby-lang.org/issues/16005#change-79666

* Author: matsuda (Akira Matsuda)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Let me propose a String to Time conversion method that can parse "yyyy-MM-dd HH:mm:ss" format, which is very much similar to `Time.iso8601`, but delimits the date part and the time part with a space character.

This format is defined as the "timestamp string" literal in SQL 92 standard: http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt (see P. 90)
and so this format is very widely used as the default datetime / timestamp literal for major existing RDBMS implementations.

Oracle
https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/Literals.html#GUID-8F4B3F82-8821-4071-84D6-FBBA21C05AC1

SQL Server
https://docs.microsoft.com/en-us/sql/odbc/reference/develop-app/date-time-and-timestamp-literals?view=sql-server-2017

PostgreSQL
https://www.postgresql.org/docs/11/datatype-datetime.html#id-1.5.7.13.19.7.2

MySQL
https://dev.mysql.com/doc/refman/8.0/en/datetime.html

SQLite3
https://www.sqlite.org/lang_datefunc.html

In order to handle this conversion in Ruby on Rails framework, we define our own String => Time conversion method
https://github.com/rails/rails/blob/b4c715fe/activemodel/lib/active_model/type/helpers/time_value.rb#L62-L76
and Time => String conversion for now,
https://github.com/rails/rails/blob/b4c715fe/activesupport/lib/active_support/core_ext/time/conversions.rb#L7-L59
and I think it's nicer if we had them in the language level with a faster implementation.

As for the method name, maybe we can name it `Time.sql92`, `Time.sql`, `Time.parse_sql92` or whatever, or maybe we can add an option to `Time.iso8601` if it could be regarded as a variation of `Time.iso8601`? (https://en.wikipedia.org/wiki/ISO_8601#cite_note-30)



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