In correct serialization of `DISTINCT ON()` syntax with postgres

[nicksrandall]

Here is the failing sql:

SELECT
   DISTINCT ON (column1) column_alias,
   column2
FROM
   table_name
ORDER BY
   column1,
   column2;

Note that this parses without errors because it parses the ON (column1) as a function.

When serializing back to string from ast, it produces:

SELECT DISTINCT ON(column1) AS column_alias, column2 FROM table_name ORDER BY column1, column2

The AS should not be there (it is an error in Postgres)

[AugustoFKL]

@nicksrandall, thanks for the report! Are you planning to work on this, or can I do that?

[nicksrandall]

@AugustoFKL go for it. I don't have bandwidth ATM.