Add postgres WINDOW keyword

Postgres allows statements of the form:
```sql
SELECT col_1, col_2, SUM(col_3) OVER w
FROM x
WINDOW w AS (PARTITION BY col_1 ORDER BY col_2)
```
where the window is defined once at the end of the query (see
https://www.postgresql.org/docs/9.5/sql-select.html).

This change adds WINDOW as a postgres keyword, preventing queries like
the above being misparsed, with table name and WINDOW being grouped into
an single identifier <Identifier 'x WINDOW'>.

0 files changed, 0 insertions, 0 deletions