On Sun, Jun 29, 2014 at 7:30 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Although printing all candidates seems to be what's preferred by > existing systems with similar facilities, I can see the point that > constructing the message in a translatable fashion might be difficult. > So personally I'd be willing to abandon insistence on that. I still > think though that printing candidates with very large distances > would be unhelpful.
Attached revision factors in everyone's concerns here, I think. I've addressed your concern about the closeness of the match proposed in the HINT - the absolute as opposed to relative quality of the match. There is a normalized distance threshold that must always be exceeded to prevent ludicrous suggestions. This works along similar lines to those sketched by Robert. Furthermore, I've made it occasionally possible to see 2 suggestions, when they're equally distant and when each suggestion comes from a different range table entry. However, if the two best suggestions (overall or within an RTE) come from within the same RTE, then that RTE is ignored for the purposes of picking a suggestion (although the lowest observed distance from an ignored RTE may still be used as the distance for later RTEs to beat to get their attributes suggested in the HINT). The idea here is that this quality-bar for suggestions doesn't come at the cost of ignoring my concern about the presumably somewhat common case where there is an unqualified and therefore ambiguous column reference that happens to also be misspelled. An ambiguous column reference and an incorrectly spelled column name are both very common, and so it seems likely that momentary lapses where the user gets both things wrong at once are also common. We do all this without going overboard, since as outlined by Robert, when there are 3 or more equally distant candidates (even if they all come from different RTEs), we give no HINT at all. The big picture here is to make mental context switches cheap when writing ad-hoc queries in psql. A lot of the HINTs that popped up in the regression tests that seemed kind of questionable no longer appear. These new measures make the coding somewhat more complex than that of the initial version, although overall the parser code added by this patch is almost entirely confined to code paths concerned only with producing diagnostic messages to help users. -- Peter Geoghegan
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