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Repair corner-case bug in array version of percentile_cont().

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The code for advancing through the input rows overlooked the case that we
might already be past the first row of the row pair now being considered,
in case the previous percentile also fell between the same two input rows.

Report and patch by Andrew Gierth; logic rewritten a bit for clarity by me.
This commit is contained in:
Tom Lane 2014-12-13 11:49:16 -05:00
parent 50f2c0687f
commit b0f479113a
3 changed files with 26 additions and 18 deletions
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34
src/backend/utils/adt/orderedsetaggs.c
View File

@ -904,42 +904,50 @@ percentile_cont_multi_final_common(FunctionCallInfo fcinfo,
for (; i < num_percentiles; i++) for (; i < num_percentiles; i++)
{ {
int64 target_row = pct_info[i].first_row; int64 first_row = pct_info[i].first_row;
bool need_lerp = (pct_info[i].second_row > target_row); int64 second_row = pct_info[i].second_row;
int idx = pct_info[i].idx; int idx = pct_info[i].idx;
/* Advance to first_row, if not already there */ /*
if (target_row > rownum) * Advance to first_row, if not already there. Note that we might
* already have rownum beyond first_row, in which case first_val
* is already correct. (This occurs when interpolating between
* the same two input rows as for the previous percentile.)
*/
if (first_row > rownum)
{ {
if (!tuplesort_skiptuples(osastate->sortstate, target_row - rownum - 1, true)) if (!tuplesort_skiptuples(osastate->sortstate, first_row - rownum - 1, true))
elog(ERROR, "missing row in percentile_cont"); elog(ERROR, "missing row in percentile_cont");
if (!tuplesort_getdatum(osastate->sortstate, true, &first_val, &isnull) || isnull) if (!tuplesort_getdatum(osastate->sortstate, true, &first_val, &isnull) || isnull)
elog(ERROR, "missing row in percentile_cont"); elog(ERROR, "missing row in percentile_cont");
rownum = target_row; rownum = first_row;
/* Always advance second_val to be latest input value */
second_val = first_val;
} }
else else if (first_row == rownum)
{ {
/* /*
* We are already at the target row, so we must previously * We are already at the desired row, so we must previously
* have read its value into second_val. * have read its value into second_val (and perhaps first_val
* as well, but this assignment is harmless in that case).
*/ */
first_val = second_val; first_val = second_val;
} }
/* Fetch second_row if needed */ /* Fetch second_row if needed */
if (need_lerp) if (second_row > rownum)
{ {
if (!tuplesort_getdatum(osastate->sortstate, true, &second_val, &isnull) || isnull) if (!tuplesort_getdatum(osastate->sortstate, true, &second_val, &isnull) || isnull)
elog(ERROR, "missing row in percentile_cont"); elog(ERROR, "missing row in percentile_cont");
rownum++; rownum++;
} }
else /* We should now certainly be on second_row exactly */
second_val = first_val; Assert(second_row == rownum);
/* Compute appropriate result */ /* Compute appropriate result */
if (need_lerp) if (second_row > first_row)
result_datum[idx] = lerpfunc(first_val, second_val, result_datum[idx] = lerpfunc(first_val, second_val,
pct_info[i].proportion); pct_info[i].proportion);
else else

6
src/test/regress/expected/aggregates.out
View File

@ -1423,11 +1423,11 @@ from tenk1;
{{NULL,999,499},{749,249,NULL}} {{NULL,999,499},{749,249,NULL}}
(1 row) (1 row)
select percentile_cont(array[0,1,0.25,0.75,0.5,1]) within group (order by x) select percentile_cont(array[0,1,0.25,0.75,0.5,1,0.3,0.32,0.35,0.38,0.4]) within group (order by x)
from generate_series(1,6) x; from generate_series(1,6) x;
percentile_cont percentile_cont
----------------------- ------------------------------------------
{1,6,2.25,4.75,3.5,6} {1,6,2.25,4.75,3.5,6,2.5,2.6,2.75,2.9,3}
(1 row) (1 row)
select ten, mode() within group (order by string4) from tenk1 group by ten; select ten, mode() within group (order by string4) from tenk1 group by ten;

2
src/test/regress/sql/aggregates.sql
View File

@ -533,7 +533,7 @@ select percentile_cont(array[0,0.25,0.5,0.75,1]) within group (order by thousand
from tenk1; from tenk1;
select percentile_disc(array[[null,1,0.5],[0.75,0.25,null]]) within group (order by thousand) select percentile_disc(array[[null,1,0.5],[0.75,0.25,null]]) within group (order by thousand)
from tenk1; from tenk1;
select percentile_cont(array[0,1,0.25,0.75,0.5,1]) within group (order by x) select percentile_cont(array[0,1,0.25,0.75,0.5,1,0.3,0.32,0.35,0.38,0.4]) within group (order by x)
from generate_series(1,6) x; from generate_series(1,6) x;
select ten, mode() within group (order by string4) from tenk1 group by ten; select ten, mode() within group (order by string4) from tenk1 group by ten;