diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index ed2d9c60d5..9301f0227d 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4003,6 +4003,15 @@ ALTER INDEX measurement_city_id_logdate_key
+
+
+ Unique constraints on partitioned tables must include all the
+ partition key columns. This limitation exists because
+ PostgreSQL can only enforce
+ uniqueness in each partition individually.
+
+
+
BEFORE ROW triggers, if necessary, must be defined