doc: clarify MERGE PARTITIONS adjacency requirement

The existing description says the ranges of merged range-partitions
"must be adjacent" only under the heading "If the DEFAULT partition is
not in the list of merged partitions".  That could be misread as
a restriction tied to the presence of a default partition.  In fact,
merging non-adjacent ranges is rejected regardless of whether
the partitioned table has a default partition; spell that out explicitly.

Also, this commit removes a small redundancy in the documentation sentence
stating that "merged range-partitions" are "to be merged".

Reported-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/aj6BPoziSb-F8aJz%40pryzbyj2023
Reported-by: Pavel Borisov <pashkin.elfe@gmail.com>
Backpatch-through: 19

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 6dd518752c003c74c49d18c271cca315a697f11b..ff7071bef5b4dbd9a2c0fc6a93d232a9f59f5a8e 100644 (file)
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -1206,7 +1206,8 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
        <listitem>
         <para>
          For range-partitioned tables, the ranges of merged partitions
-         must be adjacent in order to be merged.
+         must be adjacent; this applies even if the partitioned table
+         has no default partition.
          The partition bounds of merged partitions are combined to form the new partition bound for
          <replaceable class="parameter">partition_name</replaceable>.
         </para>