doc: Fix commas and improve spacing

doc/src/sgml/queries.sgml

@@ -1253,8 +1253,8 @@ ROLLUP ( <replaceable>e1</>, <replaceable>e2</>, <replaceable>e3</>, ... )
 GROUPING SETS (
     ( <replaceable>e1</>, <replaceable>e2</>, <replaceable>e3</>, ... ),
     ...
-    ( <replaceable>e1</>, <replaceable>e2</> )
-    ( <replaceable>e1</> )
+    ( <replaceable>e1</>, <replaceable>e2</> ),
+    ( <replaceable>e1</> ),
     ( )
 )
 </programlisting>
@@ -1282,7 +1282,7 @@ GROUPING SETS (
     (    b, c ),
     (    b    ),
     (       c ),
-    (         ),
+    (         )
 )
 </programlisting>
    </para>
@@ -1299,9 +1299,9 @@ CUBE ( (a,b), (c,d) )
     is equivalent to
 <programlisting>
 GROUPING SETS (
-    ( a, b, c, d )
-    ( a, b       )
-    (       c, d )
+    ( a, b, c, d ),
+    ( a, b       ),
+    (       c, d ),
     (            )
 )
 </programlisting>
@@ -1312,9 +1312,9 @@ ROLLUP ( a, (b,c), d )
     is equivalent to
 <programlisting>
 GROUPING SETS (
-    ( a, b, c, d )
-    ( a, b, c    )
-    ( a          )
+    ( a, b, c, d ),
+    ( a, b, c    ),
+    ( a          ),
     (            )
 )
 </programlisting>