Add from_date_string as example Trino routine

[kevinjqliu]

Description

This PR adds a new example to the Trino Routines Examples page.

The new example routine is named from_date_string. It takes a date string represented by VARCHAR and tries to best effort parse it into TIMESTAMP.
The parsing logic assumes the date string is in one of the YYYYmmdd, YYYYmmddHH, or ISO 8601 formats.

Use case: Hive table partitions are typically represented in one of these formats. It's cumbersome to figure out which date string format is used on a specific table. This routine takes care of the date string parsing regardless of the format.

Additional context and related issues

Saw https://trino.io/blog/2023/11/09/routines and wanted to give the new routines a try

Release notes

(x) This is not user-visible or is docs only, and no release notes are required.
( ) Release notes are required. Please propose a release note for me.
( ) Release notes are required, with the following suggested text:

# Section
* Fix some things. ({issue}`issuenumber`)

[kevinjqliu]

As a side note, I couldn't get nested If's to work.
Something like

    IF date_string like '%-%' THEN -- iso8601
      RETURN from_iso8601_timestamp(date_string);
    ELSE
      IF length(date_string) = 8 THEN -- YYYYmmdd
        RETURN date_parse(date_string, '%Y%m%d');
      ELSEIF length(date_string) = 10 THEN -- YYYYmmddHH
        RETURN date_parse(date_string, '%Y%m%d%H');
      END IF;
    END IF;

[mosabua]

Excellent work @kevinjqliu .. I will review and test later today

[mosabua]

As a side note, I couldn't get nested If's to work. Something like

    IF date_string like '%-%' THEN -- iso8601
      RETURN from_iso8601_timestamp(date_string);
    ELSE
      IF length(date_string) = 8 THEN -- YYYYmmdd
        RETURN date_parse(date_string, '%Y%m%d');
      ELSEIF length(date_string) = 10 THEN -- YYYYmmddHH
        RETURN date_parse(date_string, '%Y%m%d%H');
      END IF;
    END IF;

Maybe it works if you put the nested if into a separate begin/end block ..

[mosabua]

Very nice example... just a few more tweaks and gotchas to add

[kevinjqliu]

Markdown rendered using VSCode (updated to reflect the newest change)

[kevinjqliu]

BTW @mosabua, Trino SQL routines with multiple ; do not play nice in Supserset
See apache/superset#26162

[mosabua]

Yeah .. DBeaver has the same problem .. we had to update the CLI to support that as well

[kevinjqliu]

Markdown rendered using VSCode

[kevinjqliu]

@mosabua is TIMESTAMP WITH TIME ZONEW. a typo? Should it be TIMESTAMP WITH TIME ZONE. instead?
https://trino.io/docs/current/language/types.html#timestamp-with-time-zone

[mosabua]

@mosabua is TIMESTAMP WITH TIME ZONEW. a typo? Should it be TIMESTAMP WITH TIME ZONE. instead? https://trino.io/docs/current/language/types.html#timestamp-with-time-zone

Ooops .. typo from my end

[kevinjqliu]

@mosabua fixed

[mosabua]

Looks great now!

[mosabua]

Also dbeaver/dbeaver#21808