On Thu, Feb 10, 2005 at 10:30:26PM -0500, Tom Lane wrote: > Well, the point is that there are potentially three types of statements > involved: > > 1. SELECTs > 2. Utility statements that can return tuples (EXPLAIN, SHOW, etc) > 3. Utility statements that can't return tuples (ALTER, etc)
<snip> > The $64 question is whether anyone *needs* to make these distinctions. > If we arrange to return SPI_OK_SELECT for category 2, then callers won't > be able to tell the difference between categories 1 and 2, but on the > other hand a zero-row result set will still be properly classified as > a SELECT-like operation. If we leave the API as it stands today then a > zero-row result set looks like a category 3, which arguably is a worse > categorization. It occurs to me that distinguishing between 2 and 3 would be useful, since knowing if there were zero rows returned or nothing should be returned is a useful distinction. But in the general case, cases 1 and 2 can be distinguished by examining the sent query. I guess it turns out that "type-of-statement" and "returns-tuples" are orthoganal concepts and nobody realised this at the time. > I'm not sure that any of the statements in question actually can return > zero-row result sets today, but I think it would be bad to make these > decisions on the basis of assuming that the case will never arise. What's the right response to "SHOW nonexistant_variable;" ? Currently it's an error return, which seems reasonable. I can imagine that there are situations where it would be useful to be able to extract the output of VACUUM and ANALYZE as resultsets. However, there's no way for a client to signal it wants a result set. And just changing the output stops it being logged. Not an easy choice. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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