Re: support for MERGE

I suggest to reference the mvcc docs from the merge docs, or to make the merge
docs themselves include the referenced information.

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index 341fea524a1..4446e1c484e 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -425,7 +425,7 @@ COMMIT;
<para>
<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>
+ and <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
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
index f68aa09736c..99dd5814f36 100644
--- a/doc/src/sgml/ref/merge.sgml
+++ b/doc/src/sgml/ref/merge.sgml
@@ -544,6 +544,7 @@ MERGE <replaceable class="parameter">total_count</replaceable>
<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.
+ See <xref linkend="mvcc"/> for more information.
</para>
</refsect1>

Also, EXPLAIN output currently looks like this:

| Merge on ex_mtarget t (actual rows=0 loops=1)
| Tuples Inserted: 0
| Tuples Updated: 50
| Tuples Deleted: 0
| Tuples Skipped: 0

Should the "zero" rows be elided from the text output ?
And/or, should it use a more compact output format ?

There are two output formats already in use, so the options would look like
this:

Tuples: Inserted: 1 Updated: 2 Deleted: 3 Skipped: 4
or
Tuples: inserted=1 updated=2 deleted=3 skipped=4

Note double spaces and capitals.
That's separate from the question about eliding zeros.