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Implement 4 new aggregate functions from SQL2003. Specifically: var_pop(),

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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
2006-03-10 20:15:28 +00:00
parent ab812ef326
commit 0ebf1cc834
9 changed files with 418 additions and 134 deletions
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78
src/backend/utils/adt/float.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.121 2006/03/05 15:58:41 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/float.c,v 1.122 2006/03/10 20:15:25 neilc Exp $
*
*-------------------------------------------------------------------------
*/
@ -1861,11 +1861,13 @@ setseed(PG_FUNCTION_ARGS)
* FLOAT AGGREGATE OPERATORS
* =========================
*
* float8_accum - accumulate for AVG(), STDDEV(), etc
* float4_accum - same, but input data is float4
* float8_avg - produce final result for float AVG()
* float8_variance - produce final result for float VARIANCE()
* float8_stddev - produce final result for float STDDEV()
* float8_accum - accumulate for AVG(), variance aggregates, etc.
* float4_accum - same, but input data is float4
* float8_avg - produce final result for float AVG()
* float8_var_samp - produce final result for float VAR_SAMP()
* float8_var_pop - produce final result for float VAR_POP()
* float8_stddev_samp - produce final result for float STDDEV_SAMP()
* float8_stddev_pop - produce final result for float STDDEV_POP()
*
* The transition datatype for all these aggregates is a 3-element array
* of float8, holding the values N, sum(X), sum(X*X) in that order.
@ -2015,7 +2017,7 @@ float8_avg(PG_FUNCTION_ARGS)
}
Datum
float8_variance(PG_FUNCTION_ARGS)
float8_var_pop(PG_FUNCTION_ARGS)
{
ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
float8 *transvalues;
@ -2024,7 +2026,35 @@ float8_variance(PG_FUNCTION_ARGS)
sumX2,
numerator;
transvalues = check_float8_array(transarray, "float8_variance");
transvalues = check_float8_array(transarray, "float8_var_pop");
N = transvalues[0];
sumX = transvalues[1];
sumX2 = transvalues[2];
/* Population variance is undefined when N is 0, so return NULL */
if (N == 0.0)
PG_RETURN_NULL();
numerator = N * sumX2 - sumX * sumX;
/* Watch out for roundoff error producing a negative numerator */
if (numerator <= 0.0)
PG_RETURN_FLOAT8(0.0);
PG_RETURN_FLOAT8(numerator / (N * N));
}
Datum
float8_var_samp(PG_FUNCTION_ARGS)
{
ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
float8 *transvalues;
float8 N,
sumX,
sumX2,
numerator;
transvalues = check_float8_array(transarray, "float8_var_samp");
N = transvalues[0];
sumX = transvalues[1];
sumX2 = transvalues[2];
@ -2043,7 +2073,7 @@ float8_variance(PG_FUNCTION_ARGS)
}
Datum
float8_stddev(PG_FUNCTION_ARGS)
float8_stddev_pop(PG_FUNCTION_ARGS)
{
ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
float8 *transvalues;
@ -2052,7 +2082,35 @@ float8_stddev(PG_FUNCTION_ARGS)
sumX2,
numerator;
transvalues = check_float8_array(transarray, "float8_stddev");
transvalues = check_float8_array(transarray, "float8_stddev_pop");
N = transvalues[0];
sumX = transvalues[1];
sumX2 = transvalues[2];
/* Population stddev is undefined when N is 0, so return NULL */
if (N == 0.0)
PG_RETURN_NULL();
numerator = N * sumX2 - sumX * sumX;
/* Watch out for roundoff error producing a negative numerator */
if (numerator <= 0.0)
PG_RETURN_FLOAT8(0.0);
PG_RETURN_FLOAT8(sqrt(numerator / (N * N)));
}
Datum
float8_stddev_samp(PG_FUNCTION_ARGS)
{
ArrayType *transarray = PG_GETARG_ARRAYTYPE_P(0);
float8 *transvalues;
float8 N,
sumX,
sumX2,
numerator;
transvalues = check_float8_array(transarray, "float8_stddev_samp");
N = transvalues[0];
sumX = transvalues[1];
sumX2 = transvalues[2];