Trailing Comma - Snowflake

[ryaminal]

Curious what the thoughts are on supporting a trailing comma in SQL? Snowflake just announced support for this in their dialect.
Example:

SELECT emp_id,
       name,
       dept,
FROM employees;

This doesn't appear to be handled by tree-sitter-sql yet(as it was just announced) but curious if this is something tree-sitter-sql wants to support? Or would it be better to make a dialect-specific repo?

[DerekStride]

I'm up for adding it! You interested in writing the PR?

[ryaminal]

yeah, i'll give it a go. do you want it behind a flag or anything?

[DerekStride]

Adding it to the existing behaviour is good

[matthias-Q]

Not sure if I am a fan of adding the trailing comma. This is a convenience addition by snowflake and - as of now - is only supported by snowflake. It saved me more than once to see an error in the highlighting, when having a trailing comma that my query engines (postgres/impala/athena) do not accept. Since this parser does not distinguish between dialects it would not through an error.

In this particular case it would not be wise to be permissive.

[trysten]

This is what I got stuck on when attempting tree-sitter-sql in 2018
The comma is an error in practice.
test query:

SELECT
title
,
FROM
books;

MySQL 11.8.2-MariaDB-ubu2404

Error in query (1064): Syntax error near 'FROM books' at line 4

PostgreSQL 17.4 (Debian 17.4-1.pgdg120+2)

Error in query: ERROR: syntax error at or near "FROM"
LINE 4: FROM

SQLite 3.40.1

Parse error: near "FROM": syntax error
SELECT title , FROM books;
^--- error here

tree-sitter-sql fails to recognize the error. I wrote what I thought might be a reasonable test:

================================================================================
Extra Comma test
================================================================================
SELECT title, FROM Books;
--------------------------------------------------------------------------------

(program
  (statement
    (select
      (keyword_select)
      (select_expression
        (term
          (field
            (identifier)))))
    (ERROR (UNEXPECTED ','))
    (from
      (keyword_from)
      (relation
        (object_reference
          (identifier))))))

But actually working out the precedence may not be trivial.

[matthias-Q]

Oh, you are right. Nice find. I was sure it was given an error. Not sure if that got lost in some commit.