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Commit23cbeda

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Sync behavior of var_samp and stddev_samp for single NaN inputs.
var_samp(numeric) and stddev_samp(numeric) disagreed with their floatcousins about what to do for a single non-null input value that is NaN.The float versions return NULL on the grounds that the calculation isonly defined for more than one non-null input, which seems like theright answer. But the numeric versions returned NaN, as a result ofdealing with edge cases in the wrong order. Fix that. The patchalso gets rid of an insignificant memory leak in such cases.This inconsistency is of long standing, but on the whole it seems bestnot to back-patch the change into stable branches; nobody's complainedand it's such an obscure point that nobody's likely to complain.(Note that v13 and v12 now contain test cases that will notice if weaccidentally back-patch this behavior change in future.)Report and patch by me; thanks to Dean Rasheed for review.Discussion:https://postgr.es/m/353062.1591898766@sss.pgh.pa.us
1 parent03109a5 commit23cbeda

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2 files changed

+19
-20
lines changed

2 files changed

+19
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lines changed

‎src/backend/utils/adt/numeric.c

Lines changed: 17 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -5172,21 +5172,35 @@ numeric_stddev_internal(NumericAggState *state,
51725172
vsumX,
51735173
vsumX2,
51745174
vNminus1;
5175-
constNumericVar*comp;
5175+
int64totCount;
51765176
intrscale;
51775177

5178-
/* Deal with empty input and NaN-input cases */
5179-
if (state==NULL|| (state->N+state->NaNcount)==0)
5178+
/*
5179+
* Sample stddev and variance are undefined when N <= 1; population stddev
5180+
* is undefined when N == 0. Return NULL in either case (note that NaNs
5181+
* count as normal inputs for this purpose).
5182+
*/
5183+
if (state==NULL|| (totCount=state->N+state->NaNcount)==0)
5184+
{
5185+
*is_null= true;
5186+
returnNULL;
5187+
}
5188+
5189+
if (sample&&totCount <=1)
51805190
{
51815191
*is_null= true;
51825192
returnNULL;
51835193
}
51845194

51855195
*is_null= false;
51865196

5197+
/*
5198+
* Deal with NaN inputs.
5199+
*/
51875200
if (state->NaNcount>0)
51885201
returnmake_result(&const_nan);
51895202

5203+
/* OK, normal calculation applies */
51905204
init_var(&vN);
51915205
init_var(&vsumX);
51925206
init_var(&vsumX2);
@@ -5195,21 +5209,6 @@ numeric_stddev_internal(NumericAggState *state,
51955209
accum_sum_final(&(state->sumX),&vsumX);
51965210
accum_sum_final(&(state->sumX2),&vsumX2);
51975211

5198-
/*
5199-
* Sample stddev and variance are undefined when N <= 1; population stddev
5200-
* is undefined when N == 0. Return NULL in either case.
5201-
*/
5202-
if (sample)
5203-
comp=&const_one;
5204-
else
5205-
comp=&const_zero;
5206-
5207-
if (cmp_var(&vN,comp) <=0)
5208-
{
5209-
*is_null= true;
5210-
returnNULL;
5211-
}
5212-
52135212
init_var(&vNminus1);
52145213
sub_var(&vN,&const_one,&vNminus1);
52155214

‎src/test/regress/expected/aggregates.out

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -214,13 +214,13 @@ SELECT stddev_pop(3.0::numeric), stddev_samp(4.0::numeric);
214214
SELECT var_pop('nan'::numeric), var_samp('nan'::numeric);
215215
var_pop | var_samp
216216
---------+----------
217-
NaN |NaN
217+
NaN |
218218
(1 row)
219219

220220
SELECT stddev_pop('nan'::numeric), stddev_samp('nan'::numeric);
221221
stddev_pop | stddev_samp
222222
------------+-------------
223-
NaN |NaN
223+
NaN |
224224
(1 row)
225225

226226
-- verify correct results for null and NaN inputs

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