doc: improve description of privileges for MERGE and update glossary.

On the MERGE page, the description of the privileges required could be
taken to imply that the SELECT privilege is required on all columns of
the data source, whereas actually it is only required on the columns
referred to by conditions or expressions in the MERGE command. Re-word
it to make that a little clearer, and mention expressions as well as
conditions.

Also, add a glossary entry for MERGE, and nearby on the glossary page,
mention MERGE in the list of commands that cannot update a
materialized view.

Noted by Jian He. Patch by me, reviewed by Jian He.

Discussion: https://postgr.es/m/CACJufxHuSoRXKwr0MtSFLXuT2nFVWcVfEWhxg7qdP9h%2Bs3a%2BUw%40mail.gmail.com

2 files changed, 24 insertions, 7 deletions

diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml
index d6d0a3a8140..ada723a5227 100644
--- a/doc/src/sgml/glossary.sgml
+++ b/doc/src/sgml/glossary.sgml
@@ -990,8 +990,8 @@
      (just like a <glossterm linkend="glossary-view">view</glossterm>),
      but stores data in the same way that a
      <glossterm linkend="glossary-table">table</glossterm> does. It cannot be
-     modified via <command>INSERT</command>, <command>UPDATE</command>, or
-     <command>DELETE</command> operations.
+     modified via <command>INSERT</command>, <command>UPDATE</command>,
+     <command>DELETE</command>, or <command>MERGE</command> operations.
     </para>
     <para>
      For more information, see
@@ -1000,6 +1000,23 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-merge">
+   <glossterm>Merge</glossterm>
+   <glossdef>
+    <para>
+     An <acronym>SQL</acronym> command used to conditionally add, modify,
+     or remove <glossterm linkend="glossary-tuple">rows</glossterm>
+     in a given <glossterm linkend="glossary-table">table</glossterm>,
+     using data from a source
+     <glossterm linkend="glossary-relation">relation</glossterm>.
+    </para>
+    <para>
+     For more information, see
+     <xref linkend="sql-merge"/>.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-mvcc">
    <glossterm>Multi-version concurrency control (MVCC)</glossterm>
    <glossdef>
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
index 0995fe0c046..d66a0626b42 100644
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -102,14 +102,14 @@ DELETE
    that are referred to in the <literal>SET</literal> clause.
    If you specify an insert action, you must have the <literal>INSERT</literal>
    privilege on the <replaceable class="parameter">target_table_name</replaceable>.
-   If you specify an delete action, you must have the <literal>DELETE</literal>
+   If you specify a delete action, you must have the <literal>DELETE</literal>
    privilege on the <replaceable class="parameter">target_table_name</replaceable>.
    Privileges are tested once at statement start and are checked
    whether or not particular <literal>WHEN</literal> clauses are executed.
-   You will require the <literal>SELECT</literal> privilege on the
-   <replaceable class="parameter">data_source</replaceable> and any column(s)
-   of the <replaceable class="parameter">target_table_name</replaceable>
-   referred to in a <literal>condition</literal>.
+   You will require the <literal>SELECT</literal> privilege on any column(s)
+   of the <replaceable class="parameter">data_source</replaceable> and
+   <replaceable class="parameter">target_table_name</replaceable> referred to
+   in any <literal>condition</literal> or <literal>expression</literal>.
   </para>
 
   <para>