Doc: Improve clarity on partitioned table limitations

Explicitly mention that primary key constraints are also included in the
limitation that the constraint columns must be a superset of the partition key
columns.

Wording suggestion from Tom Lane.

Discussion: https://postgr.es/m/64062533.78364.1601415362244@mail.yahoo.com
Backpatch-through: 11, where unique constraints on partitioned tables were added

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 18155f1a4758d5327066ab1e1da6707a65bf2938..27922867a7aa203ca927a0429af7113b33f87e8b 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -3460,8 +3460,8 @@ ALTER INDEX measurement_city_id_logdate_key
 
      <listitem>
       <para>
-       Unique constraints on partitioned tables must include all the
-       partition key columns.  This limitation exists because
+       Unique constraints (and hence primary keys) on partitioned tables must
+       include all the partition key columns.  This limitation exists because
        <productname>PostgreSQL</productname> can only enforce
        uniqueness in each partition individually.
       </para>