[Sqlalchemy-tickets] Issue #4325: Parameters in pgsql DISTINCT ON () not getting bound (zzzeek/sqlalchemy)

[Robert B. <iss...@bi...>]

New issue 4325: Parameters in pgsql DISTINCT ON () not getting bound
https://bitbucket.org/zzzeek/sqlalchemy/issues/4325/parameters-in-pgsql-distinct-on-not

Robert Bertorelli:

Hello,

I've run into the following issue in sqlalchemy 1.2.11. I looked through the already-extant bugs and didn't find this. 

In the postgresql dialect, parameters within a DISTINCT ON clause will not be bound.

Here's a simple example using python 3.6:


```
#!python
>>> import sqlalchemy as sa
>>> from sqlalchemy.dialects import postgresql as pg
>>> col = sa.column('name')
>>> col2 = col == 'foo'
>>> sel = sa.select([col2]).distinct(col2)
>>> print(sel.compile(dialect=pg.dialect(), compile_kwargs={"literal_binds": True}))
SELECT DISTINCT ON (name = %(name_1)s) name = 'foo' AS anon_1
```

So, as you can see, the parameter in the SELECT statement (name = 'foo') did get bound properly, but the same column in the DISTINCT ON did not.

I believe that the issue can be found here:

https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/dialects/postgresql/base.py#L1528

Seems like `**kw` needs to get passed into self.process().

Thanks.