On Sun, 27 Jan 2019 at 19:17, Tom Lane <t...@sss.pgh.pa.us> wrote:
> > * Allow a normal term to match a functional index, e.g. WHERE x = > > 'abcdefgh' => WHERE substr(x, 1 , 5) = 'abcde' AND x = 'abcdefgh' > > I'm a bit confused about what you think this example means. I do > intend to work on letting extensions define rules for extracting > index clauses from function calls, because that's the requirement > that PostGIS is after in the thread that started this. I don't > know whether that would satisfy your concern, because I'm not clear > on what your concern is. > To be able to extract indexable clauses where none existed before. Hash functions assume that x = N => hash(x) = hash(N) AND x = N so I want to be able to assume x = K => f(x) = f(K) AND x = K for specific f() to allow indexable operations when we have an index on f(x) only -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
