Improve documentation of how NOT NULL works with partitioning.

Amit Langote

Discussion: http://postgr.es/m/a6f99cdb-21e7-1d65-1381-91f2cfa156e2@lab.ntt.co.jp

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 75de2262539a116cc6f270e05ff8f2a4abb63cbf..7829f378bba23e9f737ee6b240ba3369ba5cf1bb 100644 (file)
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -175,9 +175,14 @@ ALTER TABLE [ IF EXISTS ] name
      
 
      
-      If this table is a partition, one cannot perform DROP NOT NULL
+      If this table is a partition, one cannot perform DROP NOT NULLliteral>
       on a column if it is marked NOT NULL in the parent
-      table.
+      table.  To drop the NOT NULL constraint from all the
+      partitions, perform DROP NOT NULL on the parent
+      table.  Even if there is no NOT NULL constraint on the
+      parent, such a constraint can still be added to individual partitions,
+      if desired; that is, the children can disallow nulls even if the parent
+      allows them, but not the other way around.