extend indexes to accept expressions as well as columns

[jek]

indexes (postgres and mysql, at least) can be defined as expressions as well as simple column lists.

the mysql case isn't really free-form expressions ala postgres, it's 2 options (substring length, sort order) and that can be composed as an expression. so, alternately, indexes could be definable with expressions and/or per-column meta data.

a survey of other dialects would be handy, i'm a pretty rusty on their ddl.

[Mike Bayer]

here's a rudimentary patch to add it to 0.8. Needs some cleanup, as it is trying to reconcile an arbitrary SQL expression with the desire to have a simple table-bound column present - to this degree it is somewhat outgrowing ColumnCollectionMixin.

Also needs implementation for mysql, sqlite.

[Mike Bayer]

this is essentially in 7fedf9958687222a9e3c2fc4d50983711dbb3d52, with some subsequent fixes to mysql/postgresql in 44576792ab80540abbf7da88badd5bd05953c478, 6e8395c84218941c27f458a62a2120a407619dfa, 2244c3febe4a21667a842b1050fa9e3ef9d6a7ea (postgres_where has been removed, it's long deprecated).

[Mike Bayer]

Removing milestone: 0.8.0final (automated comment)