stddev() and variance() should return NULL when there is just one input

tglsfdc · tglsfdc · commit 1dc3a62ec7c9 · 2003-04-21T00:22:24.000Z
value, per recent discussion on pgsql-general.
diff --git a/src/backend/utils/adt/float.c b/src/backend/utils/adt/float.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/float.c,v 1.84 2003/03/11 21:01:33 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/float.c,v 1.85 2003/04/21 00:22:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1649,12 +1649,9 @@ float8_variance(PG_FUNCTION_ARGS)
 	sumX = transvalues[1];
 	sumX2 = transvalues[2];
 
-	/* We define VARIANCE of no values to be NULL, of 1 value to be 0 */
-	if (N == 0.0)
-		PG_RETURN_NULL();
-
+	/* Sample variance is undefined when N is 0 or 1, so return NULL */
 	if (N <= 1.0)
-		PG_RETURN_FLOAT8(0.0);
+		PG_RETURN_NULL();
 
 	numerator = N * sumX2 - sumX * sumX;
 
@@ -1680,12 +1677,9 @@ float8_stddev(PG_FUNCTION_ARGS)
 	sumX = transvalues[1];
 	sumX2 = transvalues[2];
 
-	/* We define STDDEV of no values to be NULL, of 1 value to be 0 */
-	if (N == 0.0)
-		PG_RETURN_NULL();
-
+	/* Sample stddev is undefined when N is 0 or 1, so return NULL */
 	if (N <= 1.0)
-		PG_RETURN_FLOAT8(0.0);
+		PG_RETURN_NULL();
 
 	numerator = N * sumX2 - sumX * sumX;
 
diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
@@ -14,7 +14,7 @@
  * Copyright (c) 1998-2003, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/numeric.c,v 1.59 2003/03/21 01:58:04 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/adt/numeric.c,v 1.60 2003/04/21 00:22:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1964,24 +1964,19 @@ numeric_variance(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(N) || NUMERIC_IS_NAN(sumX) || NUMERIC_IS_NAN(sumX2))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	/* We define VARIANCE of no values to be NULL, of 1 value to be 0 */
-	/* N is zero iff no digits (cf. numeric_uminus) */
-	if (N->varlen == NUMERIC_HDRSZ)
-		PG_RETURN_NULL();
-
+	/* Sample variance is undefined when N is 0 or 1, so return NULL */
 	init_var(&vN);
 	set_var_from_num(N, &vN);
 
-	init_var(&vNminus1);
-	sub_var(&vN, &const_one, &vNminus1);
-
-	if (cmp_var(&vNminus1, &const_zero) <= 0)
+	if (cmp_var(&vN, &const_one) <= 0)
 	{
 		free_var(&vN);
-		free_var(&vNminus1);
-		PG_RETURN_NUMERIC(make_result(&const_zero));
+		PG_RETURN_NULL();
 	}
 
+	init_var(&vNminus1);
+	sub_var(&vN, &const_one, &vNminus1);
+
 	init_var(&vsumX);
 	set_var_from_num(sumX, &vsumX);
 	init_var(&vsumX2);
@@ -2045,24 +2040,19 @@ numeric_stddev(PG_FUNCTION_ARGS)
 	if (NUMERIC_IS_NAN(N) || NUMERIC_IS_NAN(sumX) || NUMERIC_IS_NAN(sumX2))
 		PG_RETURN_NUMERIC(make_result(&const_nan));
 
-	/* We define STDDEV of no values to be NULL, of 1 value to be 0 */
-	/* N is zero iff no digits (cf. numeric_uminus) */
-	if (N->varlen == NUMERIC_HDRSZ)
-		PG_RETURN_NULL();
-
+	/* Sample stddev is undefined when N is 0 or 1, so return NULL */
 	init_var(&vN);
 	set_var_from_num(N, &vN);
 
-	init_var(&vNminus1);
-	sub_var(&vN, &const_one, &vNminus1);
-
-	if (cmp_var(&vNminus1, &const_zero) <= 0)
+	if (cmp_var(&vN, &const_one) <= 0)
 	{
 		free_var(&vN);
-		free_var(&vNminus1);
-		PG_RETURN_NUMERIC(make_result(&const_zero));
+		PG_RETURN_NULL();
 	}
 
+	init_var(&vNminus1);
+	sub_var(&vN, &const_one, &vNminus1);
+
 	init_var(&vsumX);
 	set_var_from_num(sumX, &vsumX);
 	init_var(&vsumX2);
