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Commit808d1f8

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Fix booltestsel() for case where we have NULL stats but not MCV stats.
In a boolean column that contains mostly nulls, ANALYZE might not findenough non-null values to populate the most-common-values stats,but it would still create a pg_statistic entry with stanullfrac set.The logic in booltestsel() for this situation did the wrong thing for"col IS NOT TRUE" and "col IS NOT FALSE" tests, forgetting that nullvalues would satisfy these tests (so that the true selectivity wouldbe close to one, not close to zero). Per bug #8274.Fix by Andrew Gierth, some comment-smithing by me.
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‎src/backend/utils/adt/selfuncs.c

Lines changed: 10 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1529,31 +1529,29 @@ booltestsel(PlannerInfo *root, BoolTestType booltesttype, Node *arg,
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/*
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* No most-common-value info available. Still have null fraction
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* information, so use it for IS [NOT] UNKNOWN. Otherwise adjust
1532-
* for null fraction and assumean even splitfor boolean tests.
1532+
* for null fraction and assumea 50-50 splitof TRUE and FALSE.
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*/
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switch (booltesttype)
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{
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caseIS_UNKNOWN:
1537-
1538-
/*
1539-
* Use freq_null directly.
1540-
*/
1537+
/* select only NULL values */
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selec=freq_null;
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break;
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caseIS_NOT_UNKNOWN:
1544-
1545-
/*
1546-
* Select not unknown (not null) values. Calculate from
1547-
* freq_null.
1548-
*/
1541+
/* select non-NULL values */
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selec=1.0-freq_null;
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break;
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caseIS_TRUE:
1552-
caseIS_NOT_TRUE:
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caseIS_FALSE:
1554-
caseIS_NOT_FALSE:
1546+
/* Assume we select half of the non-NULL values */
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selec= (1.0-freq_null) /2.0;
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break;
1549+
caseIS_NOT_TRUE:
1550+
caseIS_NOT_FALSE:
1551+
/* Assume we select NULLs plus half of the non-NULLs */
1552+
/* equiv. to freq_null + (1.0 - freq_null) / 2.0 */
1553+
selec= (freq_null+1.0) /2.0;
1554+
break;
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default:
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elog(ERROR,"unrecognized booltesttype: %d",
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(int)booltesttype);

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