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 0c2aedc361a6d6e3fa2004d2ab8139ba247abb73..1e60bdb6ef1ef23d1df6df7f4a3db6da8f455bd1 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4050,8 +4050,8 @@ ALTER INDEX measurement_city_id_logdate_key
 
      
       
-       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
        PostgreSQL can only enforce
        uniqueness in each partition individually.