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Implement 4 new aggregate functions from SQL2003. Specifically: var_pop(),
var_samp(), stddev_pop(), and stddev_samp(). var_samp() and stddev_samp() are just renamings of the historical Postgres aggregates variance() and stddev() -- the latter names have been kept for backward compatibility. This patch includes updates for the documentation and regression tests. The catversion has been bumped. NB: SQL2003 requires that DISTINCT not be specified for any of these aggregates. Per discussion on -patches, I have NOT implemented this restriction: if the user asks for stddev(DISTINCT x), presumably they know what they are doing.
This commit is contained in:
Neil Conway
@ -14,7 +14,7 @@
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* Copyright (c) 1998-2006, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.92 2006/03/05 15:58:43 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.93 2006/03/10 20:15:26 neilc Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -2181,10 +2181,22 @@ numeric_avg(PG_FUNCTION_ARGS)
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NumericGetDatum(N)));
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}
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Datum
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numeric_variance(PG_FUNCTION_ARGS)
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/*
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* Workhorse routine for the standard deviance and variance
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* aggregates. 'transarray' is the aggregate's transition
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* array. 'variance' specifies whether we should calculate the
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* variance or the standard deviation. 'sample' indicates whether the
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* caller is interested in the sample or the population
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* variance/stddev.
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*
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* If appropriate variance statistic is undefined for the input,
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* *is_null is set to true and NULL is returned.
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*/
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static Numeric
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numeric_stddev_internal(ArrayType *transarray,
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bool variance, bool sample,
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bool *is_null)
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{
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ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
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Datum *transdatums;
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int ndatums;
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Numeric N,
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@ -2195,8 +2207,11 @@ numeric_variance(PG_FUNCTION_ARGS)
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vsumX,
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vsumX2,
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vNminus1;
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NumericVar *comp;
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int rscale;
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*is_null = false;
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/* We assume the input is array of numeric */
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deconstruct_array(transarray,
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NUMERICOID, -1, false, 'i',
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@ -2208,16 +2223,26 @@ numeric_variance(PG_FUNCTION_ARGS)
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sumX2 = DatumGetNumeric(transdatums[2]);
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if (NUMERIC_IS_NAN(N) || NUMERIC_IS_NAN(sumX) || NUMERIC_IS_NAN(sumX2))
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PG_RETURN_NUMERIC(make_result(&const_nan));
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return make_result(&const_nan);
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/* Sample variance is undefined when N is 0 or 1, so return NULL */
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init_var(&vN);
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set_var_from_num(N, &vN);
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if (cmp_var(&vN, &const_one) <= 0)
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/*
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* Sample stddev and variance are undefined when N <= 1;
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* population stddev is undefined when N == 0. Return NULL in
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* either case.
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*/
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if (sample)
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comp = &const_one;
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else
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comp = &const_zero;
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if (cmp_var(&vN, comp) <= 0)
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{
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free_var(&vN);
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PG_RETURN_NULL();
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*is_null = true;
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return NULL;
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}
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init_var(&vNminus1);
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@ -2233,7 +2258,7 @@ numeric_variance(PG_FUNCTION_ARGS)
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mul_var(&vsumX, &vsumX, &vsumX, rscale); /* vsumX = sumX * sumX */
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mul_var(&vN, &vsumX2, &vsumX2, rscale); /* vsumX2 = N * sumX2 */
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sub_var(&vsumX2, &vsumX, &vsumX2); /* N * sumX2 - sumX * sumX */
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sub_var(&vsumX2, &vsumX, &vsumX2); /* N * sumX2 - sumX * sumX */
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if (cmp_var(&vsumX2, &const_zero) <= 0)
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{
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@ -2242,9 +2267,11 @@ numeric_variance(PG_FUNCTION_ARGS)
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}
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else
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{
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mul_var(&vN, &vNminus1, &vNminus1, 0); /* N * (N - 1) */
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mul_var(&vN, &vNminus1, &vNminus1, 0); /* N * (N - 1) */
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rscale = select_div_scale(&vsumX2, &vNminus1);
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div_var(&vsumX2, &vNminus1, &vsumX, rscale, true); /* variance */
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div_var(&vsumX2, &vNminus1, &vsumX, rscale, true); /* variance */
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if (!variance)
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sqrt_var(&vsumX, &vsumX, rscale); /* stddev */
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res = make_result(&vsumX);
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}
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@ -2254,86 +2281,68 @@ numeric_variance(PG_FUNCTION_ARGS)
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free_var(&vsumX);
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free_var(&vsumX2);
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PG_RETURN_NUMERIC(res);
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return res;
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}
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Datum
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numeric_stddev(PG_FUNCTION_ARGS)
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numeric_var_samp(PG_FUNCTION_ARGS)
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{
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ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
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Datum *transdatums;
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int ndatums;
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Numeric N,
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sumX,
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sumX2,
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res;
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NumericVar vN,
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vsumX,
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vsumX2,
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vNminus1;
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int rscale;
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Numeric res;
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bool is_null;
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/* We assume the input is array of numeric */
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deconstruct_array(transarray,
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NUMERICOID, -1, false, 'i',
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&transdatums, NULL, &ndatums);
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if (ndatums != 3)
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elog(ERROR, "expected 3-element numeric array");
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N = DatumGetNumeric(transdatums[0]);
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sumX = DatumGetNumeric(transdatums[1]);
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sumX2 = DatumGetNumeric(transdatums[2]);
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res = numeric_stddev_internal(PG_GETARG_ARRAYTYPE_P(0),
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true, true, &is_null);
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if (NUMERIC_IS_NAN(N) || NUMERIC_IS_NAN(sumX) || NUMERIC_IS_NAN(sumX2))
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PG_RETURN_NUMERIC(make_result(&const_nan));
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/* Sample stddev is undefined when N is 0 or 1, so return NULL */
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init_var(&vN);
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set_var_from_num(N, &vN);
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if (cmp_var(&vN, &const_one) <= 0)
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{
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free_var(&vN);
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if (is_null)
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PG_RETURN_NULL();
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}
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init_var(&vNminus1);
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sub_var(&vN, &const_one, &vNminus1);
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init_var(&vsumX);
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set_var_from_num(sumX, &vsumX);
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init_var(&vsumX2);
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set_var_from_num(sumX2, &vsumX2);
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/* compute rscale for mul_var calls */
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rscale = vsumX.dscale * 2;
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mul_var(&vsumX, &vsumX, &vsumX, rscale); /* vsumX = sumX * sumX */
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mul_var(&vN, &vsumX2, &vsumX2, rscale); /* vsumX2 = N * sumX2 */
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sub_var(&vsumX2, &vsumX, &vsumX2); /* N * sumX2 - sumX * sumX */
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if (cmp_var(&vsumX2, &const_zero) <= 0)
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{
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/* Watch out for roundoff error producing a negative numerator */
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res = make_result(&const_zero);
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}
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else
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{
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mul_var(&vN, &vNminus1, &vNminus1, 0); /* N * (N - 1) */
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rscale = select_div_scale(&vsumX2, &vNminus1);
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div_var(&vsumX2, &vNminus1, &vsumX, rscale, true); /* variance */
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sqrt_var(&vsumX, &vsumX, rscale); /* stddev */
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res = make_result(&vsumX);
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}
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free_var(&vN);
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free_var(&vNminus1);
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free_var(&vsumX);
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free_var(&vsumX2);
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PG_RETURN_NUMERIC(res);
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PG_RETURN_NUMERIC(res);
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}
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Datum
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numeric_stddev_samp(PG_FUNCTION_ARGS)
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{
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Numeric res;
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bool is_null;
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res = numeric_stddev_internal(PG_GETARG_ARRAYTYPE_P(0),
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false, true, &is_null);
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if (is_null)
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PG_RETURN_NULL();
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else
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PG_RETURN_NUMERIC(res);
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}
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Datum
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numeric_var_pop(PG_FUNCTION_ARGS)
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{
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Numeric res;
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bool is_null;
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res = numeric_stddev_internal(PG_GETARG_ARRAYTYPE_P(0),
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true, false, &is_null);
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if (is_null)
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PG_RETURN_NULL();
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else
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PG_RETURN_NUMERIC(res);
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}
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Datum
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numeric_stddev_pop(PG_FUNCTION_ARGS)
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{
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Numeric res;
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bool is_null;
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res = numeric_stddev_internal(PG_GETARG_ARRAYTYPE_P(0),
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false, false, &is_null);
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if (is_null)
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PG_RETURN_NULL();
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else
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PG_RETURN_NUMERIC(res);
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}
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/*
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* SUM transition functions for integer datatypes.
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