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由 Tom Lane 提交于
MIN/MAX not be converted to use an index if the query WHERE clause contains any volatile functions or subplans. I had originally feared that the conversion might alter the behavior of such a query with respect to a volatile function. Well, so it might, but only in the sense that the function would get evaluated at a subset of the table rows rather than all of them --- and we have never made any such guarantee anyway. (For instance, we don't refuse to use an index for an ordinary non-aggregate query when one of the non-indexable filter conditions contains a volatile function.) The prohibition against subplans was because of worry that that case wasn't adequately tested, which it wasn't, but it turns out to be possible to make 8.1 fail anyway: regression=# select o.ten, (select max(unique2) from tenk1 i where ten = o.ten or ten = (select f1 from int4_tbl limit 1)) from tenk1 o; ERROR: direct correlated subquery unsupported as initplan This is due to bogus code in SS_make_initplan_from_plan (it's an initplan, ergo it can't have any parParams). Having fixed that, we might as well allow subplans as well as initplans.
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