doc: clarify that "excluded" ON CONFLICT is a single row

Original patch by David G. Johnston.

Reported-by: David G. Johnston

Discussion: https://postgr.es/m/CAKFQuwa4J0+WuO7kW1PLbjoEvzPN+Q_j+P2bXxNnCLaszY7ZdQ@mail.gmail.com

Backpatch-through: 10

doc/src/sgml/ref/insert.sgml

@@ -181,7 +181,7 @@ INSERT INTO <replaceable class="parameter">table_name</replaceable> [ AS <replac
         provided, it completely hides the actual name of the table.
         This is particularly useful when <literal>ON CONFLICT DO UPDATE</literal>
         targets a table named <varname>excluded</varname>, since that will otherwise
-        be taken as the name of the special table representing rows proposed
+        be taken as the name of the special table representing the row proposed
         for insertion.
        </para>
       </listitem>
@@ -401,7 +401,7 @@ INSERT INTO <replaceable class="parameter">table_name</replaceable> [ AS <replac
         conflict.  The <literal>SET</literal> and
         <literal>WHERE</literal> clauses in <literal>ON CONFLICT DO
         UPDATE</literal> have access to the existing row using the
-        table's name (or an alias), and to rows proposed for insertion
+        table's name (or an alias), and to the row proposed for insertion
         using the special <varname>excluded</varname> table.
         <literal>SELECT</literal> privilege is required on any column in the
         target table where corresponding <varname>excluded</varname>