Revert MERGE patch

This reverts commits d204ef63776b8a00ca220adec23979091564e465,
83454e3c2b28141c0db01c7d2027e01040df5249 and a few more commits thereafter
(complete list at the end) related to MERGE feature.

While the feature was fully functional, with sufficient test coverage and
necessary documentation, it was felt that some parts of the executor and
parse-analyzer can use a different design and it wasn't possible to do that in
the available time. So it was decided to revert the patch for PG11 and retry
again in the future.

Thanks again to all reviewers and bug reporters.

List of commits reverted, in reverse chronological order:

 f1464c5380 Improve parse representation for MERGE
 ddb4158579 MERGE syntax diagram correction
 530e69e59b Allow cpluspluscheck to pass by renaming variable
 01b88b4df5 MERGE minor errata
 3af7b2b0d4 MERGE fix variable warning in non-assert builds
 a5d86181ec MERGE INSERT allows only one VALUES clause
 4b2d44031f MERGE post-commit review
 4923550c20 Tab completion for MERGE
 aa3faa3c7a WITH support in MERGE
 83454e3c2b New files for MERGE
 d204ef6377 MERGE SQL Command following SQL:2016

Author: Pavan Deolasee
Reviewed-by: Michael Paquier

9 files changed, 6 insertions, 690 deletions

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index 1626999a701..800e68a19e0 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -3917,11 +3917,9 @@ char *PQcmdTuples(PGresult *res);
        <structname>PGresult</structname>. This function can only be used following
        the execution of a <command>SELECT</command>, <command>CREATE TABLE AS</command>,
        <command>INSERT</command>, <command>UPDATE</command>, <command>DELETE</command>,
-       <command>MERGE</command>, <command>MOVE</command>, <command>FETCH</command>,
-       or <command>COPY</command> statement, or an <command>EXECUTE</command> of a
-       prepared query that contains an <command>INSERT</command>,
-       <command>UPDATE</command>, <command>DELETE</command>
-       or <command>MERGE</command> statement.
+       <command>MOVE</command>, <command>FETCH</command>, or <command>COPY</command> statement,
+       or an <command>EXECUTE</command> of a prepared query that contains an
+       <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> statement.
        If the command that generated the <structname>PGresult</structname> was anything
        else, <function>PQcmdTuples</function> returns an empty string. The caller
        should not free the return value directly. It will be freed when
diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index 0e3e89af560..24613e3c754 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -423,31 +423,6 @@ COMMIT;
    </para>
 
    <para>
-    The <command>MERGE</command> allows the user to specify various combinations
-    of <command>INSERT</command>, <command>UPDATE</command> or
-    <command>DELETE</command> subcommands. A <command>MERGE</command> command
-    with both <command>INSERT</command> and <command>UPDATE</command>
-    subcommands looks similar to <command>INSERT</command> with an
-    <literal>ON CONFLICT DO UPDATE</literal> clause but does not guarantee
-    that either <command>INSERT</command> and <command>UPDATE</command> will occur.
-
-    If MERGE attempts an UPDATE or DELETE and the row is concurrently updated
-    but the join condition still passes for the current target and the current
-    source tuple, then MERGE will behave the same as the UPDATE or DELETE commands
-    and perform its action on the latest version of the row, using standard
-    EvalPlanQual. MERGE actions can be conditional, so conditions must be
-    re-evaluated on the latest row, starting from the first action.
-
-    On the other hand, if the row is concurrently updated or deleted so that
-    the join condition fails, then MERGE will execute a NOT MATCHED action, if it
-    exists and the AND WHEN qual evaluates to true.
-
-    If MERGE attempts an INSERT and a unique index is present and a duplicate
-    row is concurrently inserted then a uniqueness violation is raised. MERGE
-    does not attempt to avoid the ERROR by attempting an UPDATE.
-   </para>
-
-   <para>
     Because Read Committed mode starts each command with a new snapshot
     that includes all transactions committed up to that instant,
     subsequent commands in the same transaction will see the effects
@@ -925,8 +900,7 @@ ERROR:  could not serialize access due to read/write dependencies among transact
 
         <para>
          The commands <command>UPDATE</command>,
-         <command>DELETE</command>, <command>INSERT</command> and
-         <command>MERGE</command>
+         <command>DELETE</command>, and <command>INSERT</command>
          acquire this lock mode on the target table (in addition to
          <literal>ACCESS SHARE</literal> locks on any other referenced
          tables).  In general, this lock mode will be acquired by any
diff --git a/doc/src/sgml/plpgsql.sgml b/doc/src/sgml/plpgsql.sgml
index 59f6112b07c..5b2aac618e3 100644
--- a/doc/src/sgml/plpgsql.sgml
+++ b/doc/src/sgml/plpgsql.sgml
@@ -1246,7 +1246,7 @@ EXECUTE format('SELECT count(*) FROM %I '
 </programlisting>
      Another restriction on parameter symbols is that they only work in
      <command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, and
-     <command>DELETE</command> and <command>MERGE</command> commands.  In other statement
+     <command>DELETE</command> commands.  In other statement
      types (generically called utility statements), you must insert
      values textually even if they are just data values.
     </para>
@@ -1529,7 +1529,6 @@ GET DIAGNOSTICS integer_var = ROW_COUNT;
           <listitem>
            <para>
             <command>UPDATE</command>, <command>INSERT</command>, and <command>DELETE</command>
-            and <command>MERGE</command>
             statements set <literal>FOUND</literal> true if at least one
             row is affected, false if no row is affected.
            </para>
diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml
index 7cd6ee85dc9..c81c87ef41c 100644
--- a/doc/src/sgml/ref/allfiles.sgml
+++ b/doc/src/sgml/ref/allfiles.sgml
@@ -159,7 +159,6 @@ Complete list of usable sgml source files in this directory.
 <!ENTITY load               SYSTEM "load.sgml">
 <!ENTITY lock               SYSTEM "lock.sgml">
 <!ENTITY move               SYSTEM "move.sgml">
-<!ENTITY merge              SYSTEM "merge.sgml">
 <!ENTITY notify             SYSTEM "notify.sgml">
 <!ENTITY prepare            SYSTEM "prepare.sgml">
 <!ENTITY prepareTransaction SYSTEM "prepare_transaction.sgml">
diff --git a/doc/src/sgml/ref/create_policy.sgml b/doc/src/sgml/ref/create_policy.sgml
index 32f39a48ba9..0e35b0ef43e 100644
--- a/doc/src/sgml/ref/create_policy.sgml
+++ b/doc/src/sgml/ref/create_policy.sgml
@@ -94,13 +94,6 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
    exist, a <quote>default deny</quote> policy is assumed, so that no rows will
    be visible or updatable.
   </para>
-
-  <para>
-   No separate policy exists for <command>MERGE</command>. Instead policies
-   defined for <literal>SELECT</literal>, <literal>INSERT</literal>,
-   <literal>UPDATE</literal> and <literal>DELETE</literal> are applied
-   while executing MERGE, depending on the actions that are activated.
-  </para>
  </refsect1>
 
  <refsect1>
diff --git a/doc/src/sgml/ref/insert.sgml b/doc/src/sgml/ref/insert.sgml
index da294aaa46a..62e142fd8ef 100644
--- a/doc/src/sgml/ref/insert.sgml
+++ b/doc/src/sgml/ref/insert.sgml
@@ -579,13 +579,6 @@ INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</repl
    is a partition, an error will occur if one of the input rows violates
    the partition constraint.
   </para>
-
-  <para>
-   You may also wish to consider using <command>MERGE</command>, since that
-   allows mixed <command>INSERT</command>, <command>UPDATE</command> and
-   <command>DELETE</command> within a single statement.
-   See <xref linkend="sql-merge"/>.
-  </para>
  </refsect1>
 
  <refsect1>
@@ -756,9 +749,7 @@ INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International')
    Also, the case in
    which a column name list is omitted, but not all the columns are
    filled from the <literal>VALUES</literal> clause or <replaceable>query</replaceable>,
-   is disallowed by the standard. If you prefer a more SQL Standard
-   conforming statement than <literal>ON CONFLICT</literal>, see
-   <xref linkend="sql-merge"/>.
+   is disallowed by the standard.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
deleted file mode 100644
index b2a9f67cfa9..00000000000
--- a/doc/src/sgml/ref/merge.sgml
+++ /dev/null
@@ -1,617 +0,0 @@
-<!--
-doc/src/sgml/ref/merge.sgml
-PostgreSQL documentation
--->
-
-<refentry id="sql-merge">
-
- <refmeta>
-  <refentrytitle>MERGE</refentrytitle>
-  <manvolnum>7</manvolnum>
-  <refmiscinfo>SQL - Language Statements</refmiscinfo>
- </refmeta>
-
- <refnamediv>
-  <refname>MERGE</refname>
-  <refpurpose>insert, update, or delete rows of a table based upon source data</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
-<synopsis>
-[ WITH <replaceable class="parameter">with_query</replaceable> [, ...] ]
-MERGE INTO <replaceable class="parameter">target_table_name</replaceable> [ [ AS ] <replaceable class="parameter">target_alias</replaceable> ]
-USING <replaceable class="parameter">data_source</replaceable>
-ON <replaceable class="parameter">join_condition</replaceable>
-<replaceable class="parameter">when_clause</replaceable> [...]
-
-where <replaceable class="parameter">data_source</replaceable> is
-
-{ <replaceable class="parameter">source_table_name</replaceable> |
-  ( source_query )
-}
-[ [ AS ] <replaceable class="parameter">source_alias</replaceable> ]
-
-and <replaceable class="parameter">when_clause</replaceable> is
-
-{ WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> } |
-  WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING }
-}
-
-and <replaceable class="parameter">merge_insert</replaceable> is
-
-INSERT [( <replaceable class="parameter">column_name</replaceable> [, ...] )]
-[ OVERRIDING { SYSTEM | USER } VALUE ]
-{ VALUES ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] ) | DEFAULT VALUES }
-
-and <replaceable class="parameter">merge_update</replaceable> is
-
-UPDATE SET { <replaceable class="parameter">column_name</replaceable> = { <replaceable class="parameter">expression</replaceable> | DEFAULT } |
-             ( <replaceable class="parameter">column_name</replaceable> [, ...] ) = ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] )
-           } [, ...]
-
-and <replaceable class="parameter">merge_delete</replaceable> is
-
-DELETE
-</synopsis>
- </refsynopsisdiv>
-
- <refsect1>
-  <title>Description</title>
-
-  <para>
-   <command>MERGE</command> performs actions that modify rows in the
-   <replaceable class="parameter">target_table_name</replaceable>,
-   using the <replaceable class="parameter">data_source</replaceable>.
-   <command>MERGE</command> provides a single <acronym>SQL</acronym>
-   statement that can conditionally <command>INSERT</command>,
-   <command>UPDATE</command> or <command>DELETE</command> rows, a task
-   that would otherwise require multiple procedural language statements.
-  </para>
-
-  <para>
-   First, the <command>MERGE</command> command performs a join
-   from <replaceable class="parameter">data_source</replaceable> to
-   <replaceable class="parameter">target_table_name</replaceable>
-   producing zero or more candidate change rows.  For each candidate change
-   row the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal> is set
-   just once, after which <literal>WHEN</literal> clauses are evaluated
-   in the order specified. If one of them is activated, the specified
-   action occurs. No more than one <literal>WHEN</literal> clause can be
-   activated for any candidate change row.  
-  </para>
-
-  <para>
-   <command>MERGE</command> actions have the same effect as
-   regular <command>UPDATE</command>, <command>INSERT</command>, or
-   <command>DELETE</command> commands of the same names. The syntax of
-   those commands is different, notably that there is no <literal>WHERE</literal>
-   clause and no tablename is specified.  All actions refer to the
-   <replaceable class="parameter">target_table_name</replaceable>,
-   though modifications to other tables may be made using triggers.
-  </para>
-
-  <para>
-   When <literal>DO NOTHING</literal> action is specified, the source row is
-   skipped. Since actions are evaluated in the given order, <literal>DO
-   NOTHING</literal> can be handy to skip non-interesting source rows before
-   more fine-grained handling.
-  </para>
-
-  <para>
-   There is no MERGE privilege.  
-   You must have the <literal>UPDATE</literal> privilege on the column(s)
-   of the <replaceable class="parameter">target_table_name</replaceable>
-   referred to in the <literal>SET</literal> clause
-   if you specify an update action, the <literal>INSERT</literal> privilege
-   on the <replaceable class="parameter">target_table_name</replaceable>
-   if you specify an insert action and/or the <literal>DELETE</literal>
-   privilege on the <replaceable class="parameter">target_table_name</replaceable>
-   if you specify a delete action 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 activated
-   during the subsequent execution.
-   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>.
-  </para>
-
-  <para>
-   MERGE is not supported if the <replaceable
-   class="parameter">target_table_name</replaceable> has
-   <literal>RULES</literal> defined on it.
-   See <xref linkend="rules"/> for more information about <literal>RULES</literal>.
-  </para>
- </refsect1>
-
- <refsect1>
-  <title>Parameters</title>
-
-  <variablelist>
-   <varlistentry>
-    <term><replaceable class="parameter">target_table_name</replaceable></term>
-    <listitem>
-     <para>
-      The name (optionally schema-qualified) of the target table to merge into.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">target_alias</replaceable></term>
-    <listitem>
-     <para>
-      A substitute name for the target table. When an alias is
-      provided, it completely hides the actual name of the table.  For
-      example, given <literal>MERGE foo AS f</literal>, the remainder of the
-      <command>MERGE</command> statement must refer to this table as
-      <literal>f</literal> not <literal>foo</literal>.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">source_table_name</replaceable></term>
-    <listitem>
-     <para>
-      The name (optionally schema-qualified) of the source table, view or
-      transition table.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">source_query</replaceable></term>
-    <listitem>
-     <para>
-      A query (<command>SELECT</command> statement or <command>VALUES</command>
-      statement) that supplies the rows to be merged into the
-      <replaceable class="parameter">target_table_name</replaceable>.
-      Refer to the <xref linkend="sql-select"/>
-      statement or <xref linkend="sql-values"/>
-      statement for a description of the syntax.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">source_alias</replaceable></term>
-    <listitem>
-     <para>
-      A substitute name for the data source. When an alias is
-      provided, it completely hides whether table or query was specified.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">join_condition</replaceable></term>
-    <listitem>
-     <para>
-      <replaceable class="parameter">join_condition</replaceable> is
-      an expression resulting in a value of type
-      <type>boolean</type> (similar to a <literal>WHERE</literal>
-      clause) that specifies which rows in the 
-      <replaceable class="parameter">data_source</replaceable>
-      match rows in the
-      <replaceable class="parameter">target_table_name</replaceable>.
-     </para>
-     <warning>
-      <para>
-       Only columns from <replaceable class="parameter">target_table_name</replaceable>
-       that attempt to match <replaceable class="parameter">data_source</replaceable>
-       rows should appear in <replaceable class="parameter">join_condition</replaceable>.
-       <replaceable class="parameter">join_condition</replaceable> subexpressions that
-       only reference <replaceable class="parameter">target_table_name</replaceable>
-       columns can only affect which action is taken, often in surprising ways.
-      </para>
-     </warning>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">when_clause</replaceable></term>
-    <listitem>
-     <para>
-      At least one <literal>WHEN</literal> clause is required.
-     </para>
-     <para>
-      If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
-      and the candidate change row matches a row in the
-      <replaceable class="parameter">target_table_name</replaceable>
-      the <literal>WHEN</literal> clause is activated if the
-      <replaceable class="parameter">condition</replaceable> is
-      absent or is present and evaluates to <literal>true</literal>.
-      If the <literal>WHEN</literal> clause specifies <literal>WHEN NOT MATCHED</literal>
-      and the candidate change row does not match a row in the
-      <replaceable class="parameter">target_table_name</replaceable>
-      the <literal>WHEN</literal> clause is activated if the
-      <replaceable class="parameter">condition</replaceable> is
-      absent or is present and evaluates to <literal>true</literal>.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">condition</replaceable></term>
-    <listitem>
-     <para>
-      An expression that returns a value of type <type>boolean</type>.
-      If this expression returns <literal>true</literal> then the <literal>WHEN</literal>
-      clause will be activated and the corresponding action will occur for
-      that row. The expression may not contain functions that possibly performs
-      writes to the database.
-     </para>
-     <para>
-      A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
-      in both the source and the target relation. A condition on a
-      <literal>WHEN NOT MATCHED</literal> clause can only refer to columns from
-      the source relation, since by definition there is no matching target row.
-      Only the system attributes from the target table are accessible.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">merge_insert</replaceable></term>
-    <listitem>
-     <para>
-      The specification of an <literal>INSERT</literal> action that inserts
-      one row into the target table.
-      The target column names can be listed in any order. If no list of
-      column names is given at all, the default is all the columns of the
-      table in their declared order.
-     </para>
-     <para>
-      Each column not present in the explicit or implicit column list will be
-      filled with a default value, either its declared default value
-      or null if there is none.
-     </para>
-     <para>
-      If the expression for any column is not of the correct data type,
-      automatic type conversion will be attempted.
-     </para>
-     <para>
-      If <replaceable class="parameter">target_table_name</replaceable>
-      is a partitioned table, each row is routed to the appropriate partition
-      and inserted into it.
-      If <replaceable class="parameter">target_table_name</replaceable>
-      is a partition, an error will occur if one of the input rows violates
-      the partition constraint.
-     </para>
-     <para>
-      Column names may not be specified more than once.
-      <command>INSERT</command> actions cannot contain sub-selects. 
-     </para>
-     <para>
-      Only one <literal>VALUES</literal> clause can be specified.
-      The <literal>VALUES</literal> clause can only refer to columns from
-      the source relation, since by definition there is no matching target row.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">merge_update</replaceable></term>
-    <listitem>
-     <para>
-      The specification of an <literal>UPDATE</literal> action that updates
-      the current row of the <replaceable
-      class="parameter">target_table_name</replaceable>.
-      Column names may not be specified more than once.
-     </para>
-     <para>
-      Do not include the table name, as you would normally do with an
-      <xref linkend="sql-update"/> command.
-      For example, <literal>UPDATE tab SET col = 1</literal> is invalid. Also,
-      do not include a <literal>WHERE</literal> clause, since only the current
-      row can be updated. For example,
-      <literal>UPDATE SET col = 1 WHERE key = 57</literal> is invalid.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">merge_delete</replaceable></term>
-    <listitem>
-     <para>
-      Specifies a <literal>DELETE</literal> action that deletes the current row
-      of the <replaceable class="parameter">target_table_name</replaceable>.
-      Do not include the tablename or any other clauses, as you would normally
-      do with an <xref linkend="sql-delete"/> command.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">column_name</replaceable></term>
-    <listitem>
-     <para>
-      The name of a column in the <replaceable
-      class="parameter">target_table_name</replaceable>.  The column name
-      can be qualified with a subfield name or array subscript, if
-      needed.  (Inserting into only some fields of a composite
-      column leaves the other fields null.)  When referencing a
-      column, do not include the table's name in the specification
-      of a target column.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>OVERRIDING SYSTEM VALUE</literal></term>
-    <listitem>
-     <para>
-      Without this clause, it is an error to specify an explicit value
-      (other than <literal>DEFAULT</literal>) for an identity column defined
-      as <literal>GENERATED ALWAYS</literal>.  This clause overrides that
-      restriction.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>OVERRIDING USER VALUE</literal></term>
-    <listitem>
-     <para>
-      If this clause is specified, then any values supplied for identity
-      columns defined as <literal>GENERATED BY DEFAULT</literal> are ignored
-      and the default sequence-generated values are applied.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>DEFAULT VALUES</literal></term>
-    <listitem>
-     <para>
-      All columns will be filled with their default values.
-      (An <literal>OVERRIDING</literal> clause is not permitted in this
-      form.)
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">expression</replaceable></term>
-    <listitem>
-     <para>
-      An expression to assign to the column.  The expression can use the
-      old values of this and other columns in the table.
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><literal>DEFAULT</literal></term>
-    <listitem>
-     <para>
-      Set the column to its default value (which will be NULL if no
-      specific default expression has been assigned to it).
-     </para>
-    </listitem>
-   </varlistentry>
-
-   <varlistentry>
-    <term><replaceable class="parameter">with_query</replaceable></term>
-    <listitem>
-     <para>
-      The <literal>WITH</literal> clause allows you to specify one or more
-      subqueries that can be referenced by name in the <command>MERGE</command>
-      query. See <xref linkend="queries-with"/> and <xref linkend="sql-select"/>
-      for details.
-     </para>
-    </listitem>
-   </varlistentry>
-
-  </variablelist>
- </refsect1>
-
- <refsect1>
-  <title>Outputs</title>
-
-  <para>
-   On successful completion, a <command>MERGE</command> command returns a command
-   tag of the form
-<screen>
-MERGE <replaceable class="parameter">total-count</replaceable>
-</screen>
-   The <replaceable class="parameter">total-count</replaceable> is the total
-   number of rows changed (whether inserted, updated, or deleted).
-   If <replaceable class="parameter">total-count</replaceable> is 0, no rows
-   were changed in any way.
-  </para>
-
- </refsect1>
-
- <refsect1>
-  <title>Execution</title>
-
-  <para>
-   The following steps take place during the execution of
-   <command>MERGE</command>.
-    <orderedlist>
-     <listitem>
-      <para>
-       Perform any BEFORE STATEMENT triggers for all actions specified, whether or
-       not their <literal>WHEN</literal> clauses are activated during execution.
-      </para>
-     </listitem>
-     <listitem>
-      <para>
-       Perform a join from source to target table.
-       The resulting query will be optimized normally and will produce
-       a set of candidate change row. For each candidate change row
-       <orderedlist>
-        <listitem>
-         <para>
-          Evaluate whether each row is MATCHED or NOT MATCHED.
-         </para>
-        </listitem>
-        <listitem>
-         <para>
-          Test each WHEN condition in the order specified until one activates.
-         </para>
-        </listitem>
-        <listitem>
-         <para>
-          When activated, perform the following actions
-          <orderedlist>
-           <listitem>
-            <para>
-             Perform any BEFORE ROW triggers that fire for the action's event type.
-            </para>
-           </listitem>
-           <listitem>
-            <para>
-             Apply the action specified, invoking any check constraints on the
-             target table.
-             However, it will not invoke rules.
-            </para>
-           </listitem>
-           <listitem>
-            <para>
-             Perform any AFTER ROW triggers that fire for the action's event type.
-            </para>
-           </listitem>
-          </orderedlist>
-         </para>
-        </listitem>
-       </orderedlist>
-      </para>
-     </listitem>
-     <listitem>
-      <para>
-       Perform any AFTER STATEMENT triggers for actions specified, whether or
-       not they actually occur.  This is similar to the behavior of an
-       <command>UPDATE</command> statement that modifies no rows.
-      </para>
-     </listitem>
-    </orderedlist>
-   In summary, statement triggers for an event type (say, INSERT) will
-   be fired whenever we <emphasis>specify</emphasis> an action of that kind. Row-level
-   triggers will fire only for the one event type <emphasis>activated</emphasis>.
-   So a <command>MERGE</command> might fire statement triggers for both
-   <command>UPDATE</command> and <command>INSERT</command>, even though only
-   <command>UPDATE</command> row triggers were fired.
-  </para>
-
-  <para>
-   You should ensure that the join produces at most one candidate change row
-   for each target row.  In other words, a target row shouldn't join to more
-   than one data source row.  If it does, then only one of the candidate change
-   rows will be used to modify the target row, later attempts to modify will
-   cause an error.  This can also occur if row triggers make changes to the
-   target table which are then subsequently modified by <command>MERGE</command>.
-   If the repeated action is an <command>INSERT</command> this will
-   cause a uniqueness violation while a repeated <command>UPDATE</command> or
-   <command>DELETE</command> will cause a cardinality violation; the latter behavior
-   is required by the <acronym>SQL</acronym> Standard. This differs from
-   historical <productname>PostgreSQL</productname> behavior of joins in
-   <command>UPDATE</command> and <command>DELETE</command> statements where second and
-   subsequent attempts to modify are simply ignored.
-  </para>
-
-  <para>
-   If a <literal>WHEN</literal> clause omits an <literal>AND</literal> clause it becomes
-   the final reachable clause of that kind (<literal>MATCHED</literal> or
-   <literal>NOT MATCHED</literal>). If a later <literal>WHEN</literal> clause of that kind
-   is specified it would be provably unreachable and an error is raised.
-   If a final reachable clause is omitted it is possible that no action
-   will be taken for a candidate change row.
-  </para>
-
- </refsect1>
- <refsect1>
-  <title>Notes</title>
-
-  <para>
-   The order in which rows are generated from the data source is indeterminate
-   by default. A <replaceable class="parameter">source_query</replaceable>
-   can be used to specify a consistent ordering, if required, which might be
-   needed to avoid deadlocks between concurrent transactions.
-  </para>
-
-  <para>
-   There is no <literal>RETURNING</literal> clause with <command>MERGE</command>.
-   Actions of <command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command>
-   cannot contain <literal>RETURNING</literal> or <literal>WITH</literal> clauses.
-  </para>
-
-  <tip>
-   <para>
-    You may also wish to consider using <command>INSERT ... ON CONFLICT</command> as an
-    alternative statement which offers the ability to run an <command>UPDATE</command>
-    if a concurrent <command>INSERT</command> occurs.  There are a variety of
-    differences and restrictions between the two statement types and they are not
-    interchangeable.
-   </para>
-  </tip>
- </refsect1>
-
- <refsect1>
-  <title>Examples</title>
-
-  <para>
-   Perform maintenance on CustomerAccounts based upon new Transactions.
-
-<programlisting>
-MERGE CustomerAccount CA
-USING RecentTransactions T
-ON T.CustomerId = CA.CustomerId
-WHEN MATCHED THEN
-  UPDATE SET Balance = Balance + TransactionValue
-WHEN NOT MATCHED THEN
-  INSERT (CustomerId, Balance)
-  VALUES (T.CustomerId, T.TransactionValue);
-</programlisting>
-
-   notice that this would be exactly equivalent to the following
-   statement because the <literal>MATCHED</literal> result does not change
-   during execution
-
-<programlisting>
-MERGE CustomerAccount CA
-USING (Select CustomerId, TransactionValue From RecentTransactions) AS T
-ON CA.CustomerId = T.CustomerId
-WHEN NOT MATCHED THEN
-  INSERT (CustomerId, Balance)
-  VALUES (T.CustomerId, T.TransactionValue)
-WHEN MATCHED THEN
-  UPDATE SET Balance = Balance + TransactionValue;
-</programlisting>
-  </para>
-
-  <para>
-   Attempt to insert a new stock item along with the quantity of stock. If
-   the item already exists, instead update the stock count of the existing
-   item. Don't allow entries that have zero stock.
-<programlisting>
-MERGE INTO wines w
-USING wine_stock_changes s
-ON s.winename = w.winename
-WHEN NOT MATCHED AND s.stock_delta > 0 THEN
-  INSERT VALUES(s.winename, s.stock_delta)
-WHEN MATCHED AND w.stock + s.stock_delta > 0 THEN
-  UPDATE SET stock = w.stock + s.stock_delta;
-WHEN MATCHED THEN
-  DELETE;
-</programlisting>
-
-   The wine_stock_changes table might be, for example, a temporary table
-   recently loaded into the database.
-  </para>
-
- </refsect1>
-
- <refsect1>
-  <title>Compatibility</title>
-   <para>
-    This command conforms to the <acronym>SQL</acronym> standard.
-  </para>
-   <para>
-    The WITH clause and DO NOTHING action are extensions to the <acronym>SQL</acronym> standard.
-  </para>
- </refsect1>
-</refentry>
diff --git a/doc/src/sgml/reference.sgml b/doc/src/sgml/reference.sgml
index ef2270c4673..d27fb414f7c 100644
--- a/doc/src/sgml/reference.sgml
+++ b/doc/src/sgml/reference.sgml
@@ -186,7 +186,6 @@
    &listen;
    &load;
    &lock;
-   &merge;
    &move;
    &notify;
    &prepare;
diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml
index cce58fbf1d0..c43dbc9786e 100644
--- a/doc/src/sgml/trigger.sgml
+++ b/doc/src/sgml/trigger.sgml
@@ -183,26 +183,6 @@
    </para>
 
    <para>
-    No separate triggers are defined for <command>MERGE</command>. Instead,
-    statement-level or row-level <command>UPDATE</command>,
-    <command>DELETE</command> and <command>INSERT</command> triggers are fired
-    depending on what actions are specified in the <command>MERGE</command> query
-    and what actions are activated.
-   </para>
-
-   <para>
-    While running a <command>MERGE</command> command, statement-level
-    <literal>BEFORE</literal> and <literal>AFTER</literal> triggers are fired for
-    events specified in the actions of the <command>MERGE</command> command,
-    irrespective of whether the action is finally activated or not. This is same as
-    an <command>UPDATE</command> statement that updates no rows, yet
-    statement-level triggers are fired. The row-level triggers are fired only
-    when a row is actually updated, inserted or deleted. So it's perfectly legal
-    that while statement-level triggers are fired for certain type of action, no
-    row-level triggers are fired for the same kind of action.
-   </para>
-
-   <para>
     Trigger functions invoked by per-statement triggers should always
     return <symbol>NULL</symbol>. Trigger functions invoked by per-row
     triggers can return a table row (a value of