Doc: clarify behavior of standard aggregates for null inputs.

Section 4.2.7 says that unless otherwise specified, built-in
aggregates ignore rows in which any input is null.  This is
not true of the JSON aggregates, but it wasn't documented.
Fix that.

Of the other entries in table 9.55, some were explicit about
ignoring nulls, and some weren't; for consistency and
self-contained-ness, make them all say it explicitly.

Per bug #15884 from Tim Möhlmann.  Back-patch to all supported
branches.

Discussion: https://postgr.es/m/15884-c32d848f787fcae3@postgresql.org

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 8bac154d813b0099810f6e8e2cc7e8064ad5aaf5..488fd9674509f3c96af746a0750711ead3f9f4e8 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -12200,7 +12200,7 @@ NULL baz(3 rows)
        double precision for a floating-point argument,
        otherwise the same as the argument data type
       
-      the average (arithmetic mean) of all input values
+      the average (arithmetic mean) of all non-null input values
      
 
      
@@ -12320,7 +12320,7 @@ NULL baz(3 rows)
       
        json
       
-      aggregates values as a JSON array
+      aggregates values, including nulls, as a JSON array
      
 
      
@@ -12336,7 +12336,8 @@ NULL baz(3 rows)
       
        json
       
-      aggregates name/value pairs as a JSON object
+      aggregates name/value pairs as a JSON object; values can be
+       null, but not names
      
 
      
@@ -12350,7 +12351,7 @@ NULL baz(3 rows)
       same as argument type
       
        maximum value of 
-       class="parameter">expression across all input
+       class="parameter">expression across all non-null input
        values
       
      
@@ -12366,7 +12367,7 @@ NULL baz(3 rows)
       same as argument type
       
        minimum value of 
-       class="parameter">expression across all input
+       class="parameter">expression across all non-null input
        values
       
      
@@ -12387,7 +12388,7 @@ NULL baz(3 rows)
       
        same as argument types
       
-      input values concatenated into a string, separated by delimiter
+      non-null input values concatenated into a string, separated by delimiter
      
 
      
@@ -12409,7 +12410,8 @@ NULL baz(3 rows)
        bigint arguments, otherwise the same as the
        argument data type
       
-      sum of expression across all input values
+      sum of expression
+       across all non-null input values
      
 
      
@@ -12425,7 +12427,8 @@ NULL baz(3 rows)
       
        xml
       
-      concatenation of XML values (see also )
+      concatenation of non-null XML values
+       (see also )