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Teach nulltestsel() that system columns are never NULL.

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While it's perhaps unlikely that users would write an explicit test
like "ctid IS NULL", this function is also used in range estimation,
and an incorrect answer can throw off the results for tight ranges.
Anyway it's not much code so we might as well do it.

Edmund Horner

Discussion: https://postgr.es/m/CAMyN-kCa3BFUFrCTtQeprxTU1anCd3Pua7zXstGCKq4pXgjukw@mail.gmail.com
This commit is contained in:
Tom Lane
2019-01-25 11:44:26 -05:00
parent 6119060d01
commit ff750ce2d8
1 changed files with 9 additions and 0 deletions
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9
src/backend/utils/adt/selfuncs.c
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@ -1797,6 +1797,15 @@ nulltestsel(PlannerInfo *root, NullTestType nulltesttype, Node *arg,
return (Selectivity) 0; /* keep compiler quiet */
}
}
else if (vardata.var && IsA(vardata.var, Var) &&
((Var *) vardata.var)->varattno < 0)
{
/*
* There are no stats for system columns, but we know they are never
* NULL.
*/
selec = (nulltesttype == IS_NULL) ? 0.0 : 1.0;
}
else
{
/*