Doc: Miscellaneous doc updates for MERGE.

Update a few places in the documentation that should mention MERGE
among the list of applicable commands. In a couple of places, a
slightly more detailed description of what happens for MERGE seems
appropriate.

Reviewed by Alvaro Herrera.

Discussion: http://postgr.es/m/CAEZATCWqHLcxab89ATMQZNGFG_mxDPM%2BjzkSbXKD3JYPfRGvtw%40mail.gmail.com

doc/src/sgml/arch-dev.sgml

@@ -530,13 +530,15 @@
    </para>
 
    <para>
-    The executor mechanism is used to evaluate all four basic SQL query
+    The executor mechanism is used to evaluate all five basic SQL query
     types: <command>SELECT</command>, <command>INSERT</command>,
-    <command>UPDATE</command>, and <command>DELETE</command>.
+    <command>UPDATE</command>, <command>DELETE</command>, and
+    <command>MERGE</command>.
     For <command>SELECT</command>, the top-level executor code
     only needs to send each row returned by the query plan tree
     off to the client.  <command>INSERT ... SELECT</command>,
-    <command>UPDATE</command>, and <command>DELETE</command>
+    <command>UPDATE</command>, <command>DELETE</command>, and
+    <command>MERGE</command>
     are effectively <command>SELECT</command>s under a special
     top-level plan node called <literal>ModifyTable</literal>.
    </para>
@@ -552,7 +554,13 @@
     mark the old row deleted.  For <command>DELETE</command>, the only
     column that is actually returned by the plan is the TID, and the
     <literal>ModifyTable</literal> node simply uses the TID to visit each
-    target row and mark it deleted.
+    target row and mark it deleted.  For <command>MERGE</command>, the
+    planner joins the source and target relations, and includes all
+    column values required by any of the <literal>WHEN</literal> clauses,
+    plus the TID of the target row; this data is fed up to the
+    <literal>ModifyTable</literal> node, which uses the information to
+    work out which <literal>WHEN</literal> clause to execute, and then
+    inserts, updates or deletes the target row, as required.
    </para>
 
    <para>

doc/src/sgml/ddl.sgml

@@ -1777,7 +1777,8 @@ REVOKE ALL ON accounts FROM PUBLIC;
        view, or other table-like object.
        Also allows use of <command>COPY TO</command>.
        This privilege is also needed to reference existing column values in
-       <command>UPDATE</command> or <command>DELETE</command>.
+       <command>UPDATE</command>, <command>DELETE</command>,
+       or <command>MERGE</command>.
        For sequences, this privilege also allows use of the
        <function>currval</function> function.
        For large objects, this privilege allows the object to be read.

doc/src/sgml/high-availability.sgml

@@ -1617,7 +1617,8 @@ synchronous_standby_names = 'ANY 2 (s1, s2, s3)'
      <listitem>
       <para>
        Data Manipulation Language (DML): <command>INSERT</command>,
-       <command>UPDATE</command>, <command>DELETE</command>, <command>COPY FROM</command>,
+       <command>UPDATE</command>, <command>DELETE</command>,
+       <command>MERGE</command>, <command>COPY FROM</command>,
        <command>TRUNCATE</command>.
        Note that there are no allowed actions that result in a trigger
        being executed during recovery.  This restriction applies even to

doc/src/sgml/perform.sgml

@@ -788,9 +788,10 @@ ROLLBACK;
 
    <para>
     As seen in this example, when the query is an <command>INSERT</command>,
-    <command>UPDATE</command>, or <command>DELETE</command> command, the actual work of
+    <command>UPDATE</command>, <command>DELETE</command>, or
+    <command>MERGE</command> command, the actual work of
     applying the table changes is done by a top-level Insert, Update,
-    or Delete plan node.  The plan nodes underneath this node perform
+    Delete, or Merge plan node.  The plan nodes underneath this node perform
     the work of locating the old rows and/or computing the new data.
     So above, we see the same sort of bitmap table scan we've seen already,
     and its output is fed to an Update node that stores the updated rows.
@@ -803,7 +804,8 @@ ROLLBACK;
    </para>
 
    <para>
-    When an <command>UPDATE</command> or <command>DELETE</command> command affects an
+    When an <command>UPDATE</command>, <command>DELETE</command>, or
+    <command>MERGE</command> command affects an
     inheritance hierarchy, the output might look like this:
 
 <screen>

doc/src/sgml/plpgsql.sgml

@@ -1044,7 +1044,8 @@ INSERT INTO mytable VALUES (1,'one'), (2,'two');
      <application>PL/pgSQL</application> variable values can be
      automatically inserted into optimizable SQL commands, which
      are <command>SELECT</command>, <command>INSERT</command>,
-     <command>UPDATE</command>, <command>DELETE</command>, and certain
+     <command>UPDATE</command>, <command>DELETE</command>,
+     <command>MERGE</command>, and certain
      utility commands that incorporate one of these, such
      as <command>EXPLAIN</command> and <command>CREATE TABLE ... AS
      SELECT</command>.  In these commands,

doc/src/sgml/protocol.sgml

@@ -4110,6 +4110,13 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
         <replaceable>rows</replaceable> is the number of rows updated.
        </para>
 
+       <para>
+        For a <command>MERGE</command> command, the tag is
+        <literal>MERGE <replaceable>rows</replaceable></literal> where
+        <replaceable>rows</replaceable> is the number of rows inserted,
+        updated, or deleted.
+       </para>
+
        <para>
         For a <command>SELECT</command> or <command>CREATE TABLE AS</command>
         command, the tag is <literal>SELECT <replaceable>rows</replaceable></literal>

doc/src/sgml/queries.sgml

@@ -2058,8 +2058,8 @@ SELECT <replaceable>select_list</replaceable> FROM <replaceable>table_expression
    in a <literal>WITH</literal> clause can be a <command>SELECT</command>,
    <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command>; and the
    <literal>WITH</literal> clause itself is attached to a primary statement that can
-   also be a <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, or
-   <command>DELETE</command>.
+   be a <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>,
+   <command>DELETE</command>, or <command>MERGE</command>.
   </para>
 
  <sect2 id="queries-with-select">
@@ -2581,7 +2581,8 @@ SELECT * FROM w AS w1 JOIN w AS w2 ON w1.f = w2.f;
   <para>
    The examples above only show <literal>WITH</literal> being used with
    <command>SELECT</command>, but it can be attached in the same way to
-   <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command>.
+   <command>INSERT</command>, <command>UPDATE</command>,
+   <command>DELETE</command>, or <command>MERGE</command>.
    In each case it effectively provides temporary table(s) that can
    be referred to in the main command.
   </para>
@@ -2591,8 +2592,9 @@ SELECT * FROM w AS w1 JOIN w AS w2 ON w1.f = w2.f;
    <title>Data-Modifying Statements in <literal>WITH</literal></title>
 
    <para>
-    You can use data-modifying statements (<command>INSERT</command>,
-    <command>UPDATE</command>, or <command>DELETE</command>) in <literal>WITH</literal>.  This
+    You can use most data-modifying statements (<command>INSERT</command>,
+    <command>UPDATE</command>, or <command>DELETE</command>, but not
+    <command>MERGE</command>) in <literal>WITH</literal>.  This
     allows you to perform several different operations in the same query.
     An example is:
 

doc/src/sgml/ref/create_publication.sgml

@@ -299,6 +299,12 @@ CREATE PUBLICATION <replaceable class="parameter">name</replaceable>
    <command>UPDATE</command>, or it may not be published at all.
   </para>
 
+  <para>
+   For a <command>MERGE</command> command, the publication will publish an
+   <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command>
+   for each row inserted, updated, or deleted.
+  </para>
+
   <para>
    <command>ATTACH</command>ing a table into a partition tree whose root is
    published using a publication with <literal>publish_via_partition_root</literal>

doc/src/sgml/ref/explain.sgml

@@ -94,7 +94,8 @@ EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replac
     statement will happen as usual.  If you wish to use
     <command>EXPLAIN ANALYZE</command> on an
     <command>INSERT</command>, <command>UPDATE</command>,
-    <command>DELETE</command>, <command>CREATE TABLE AS</command>,
+    <command>DELETE</command>, <command>MERGE</command>,
+    <command>CREATE TABLE AS</command>,
     or <command>EXECUTE</command> statement
     without letting the command affect your data, use this approach:
 <programlisting>
@@ -272,7 +273,8 @@ ROLLBACK;
     <listitem>
      <para>
       Any <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>,
-      <command>DELETE</command>, <command>VALUES</command>, <command>EXECUTE</command>,
+      <command>DELETE</command>, <command>MERGE</command>,
+      <command>VALUES</command>, <command>EXECUTE</command>,
       <command>DECLARE</command>, <command>CREATE TABLE AS</command>, or
       <command>CREATE MATERIALIZED VIEW AS</command> statement, whose execution
       plan you wish to see.

doc/src/sgml/ref/prepare.sgml

@@ -116,7 +116,8 @@ PREPARE <replaceable class="parameter">name</replaceable> [ ( <replaceable class
     <listitem>
      <para>
       Any <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>,
-      <command>DELETE</command>, or <command>VALUES</command> statement.
+      <command>DELETE</command>, <command>MERGE</command>, or <command>VALUES</command>
+      statement.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/set_transaction.sgml

@@ -121,7 +121,8 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
    The transaction isolation level cannot be changed after the first query or
    data-modification statement (<command>SELECT</command>,
    <command>INSERT</command>, <command>DELETE</command>,
-   <command>UPDATE</command>, <command>FETCH</command>, or
+   <command>UPDATE</command>, <command>MERGE</command>,
+   <command>FETCH</command>, or
    <command>COPY</command>) of a transaction has been executed.  See
    <xref linkend="mvcc"/> for more information about transaction
    isolation and concurrency control.
@@ -131,8 +132,9 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
    The transaction access mode determines whether the transaction is
    read/write or read-only.  Read/write is the default.  When a
    transaction is read-only, the following SQL commands are
-   disallowed: <literal>INSERT</literal>, <literal>UPDATE</literal>,
-   <literal>DELETE</literal>, and <literal>COPY FROM</literal> if the
+   disallowed: <command>INSERT</command>, <command>UPDATE</command>,
+   <command>DELETE</command>, <command>MERGE</command>, and
+   <command>COPY FROM</command> if the
    table they would write to is not a temporary table; all
    <literal>CREATE</literal>, <literal>ALTER</literal>, and
    <literal>DROP</literal> commands; <literal>COMMENT</literal>,
@@ -169,7 +171,8 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
    start of a transaction, before the first query or
    data-modification statement (<command>SELECT</command>,
    <command>INSERT</command>, <command>DELETE</command>,
-   <command>UPDATE</command>, <command>FETCH</command>, or
+   <command>UPDATE</command>, <command>MERGE</command>,
+   <command>FETCH</command>, or
    <command>COPY</command>) of the transaction.  Furthermore, the transaction
    must already be set to <literal>SERIALIZABLE</literal> or
    <literal>REPEATABLE READ</literal> isolation level (otherwise, the snapshot

doc/src/sgml/xfunc.sgml

@@ -186,7 +186,8 @@
      language can be packaged together and defined as a function.
      Besides <command>SELECT</command> queries, the commands can include data
      modification queries (<command>INSERT</command>,
-     <command>UPDATE</command>, and <command>DELETE</command>), as well as
+     <command>UPDATE</command>, <command>DELETE</command>, and
+     <command>MERGE</command>), as well as
      other SQL commands. (You cannot use transaction control commands, e.g.,
      <command>COMMIT</command>, <command>SAVEPOINT</command>, and some utility
      commands, e.g.,  <literal>VACUUM</literal>, in <acronym>SQL</acronym> functions.)