PG EXTRACT is broken

[Mike Bayer]

is hardcoded to timestamp and doesn't work if the given expression is ultimately interval, or is text().

[Mike Bayer]

patch attached.

[Mike Bayer]

so the datetime + datetime and similar are invalid - you can't add two dates/datetimes/times, only subtract. intervals can be added and subtracted and date+time can too. the functionality and tests should take into account all of: http://www.postgresql.org/docs/current/static/functions-datetime.html

[Mike Bayer]

using the patch as a starting point, moved the rules to be data driven and based off the PG chart. fix is in 4acf0f69f394c151b2e6c2d399632888cdef6fd9 cf7c80b3f4a2ed9e2d2d2dd814839b9f50048815.

[Mike Bayer]

Removing milestone: 0.5.8 (automated comment)