Hi,

Given a quick glance, it looks ok, thanks.
Could you add a test using a range that's not numeric? I'll suggest where it could be added later

places were we could use a test:

• sqlalchemy/test/sql/test_functions.py

  Line 805 in 7ab6344

  def test_funcfilter_windowing_range(self):

  add also a range with say text, like ('a', 'e')
• a new test case here that would use the range on a new text column

  sqlalchemy/lib/sqlalchemy/testing/suite/test_select.py

  Line 1903 in 7ab6344

  class WindowFunctionTest(fixtures.TablesTest):

places were we could use a test:

Added in 00afd4f.

Some problems I noticed:

• I'd really like to be completely type agnostic, allowing for example interval ranges, but I haven't found a correct way to handle _type on the literal in _FrameClause.__init__ in that case.
• I'd prefer to have a separate parameter saying whether each end of the range is PRECEDING or FOLLOWING, but I didn't want to make that large of a change. This would allow types that don't have a concept of "greater than" or "less than" zero... although I'm not actually sure whether any dialect allows them in RANGE.
• I couldn't think of any valid "BETWEEN 'a' PRECEDING and 'e' FOLLOWING"-type syntax, so I used Float rather than string.

Any input on my comments above? Alternatively, what do you all think about merging the changes as-is to at least handle fractional numeric values?

sorry, haven't had time to re-look at this. I'll make it run the full ci at least

New Gerrit review created for change a779c37: https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset 897929e added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset c373341 added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset 794e265 added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset baa70bf added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset 1bc7261 added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022

Patchset 8063cec added to existing Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/6022