Clarify trigger function return convention, per Thomas Hallgren.

diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml
index a8ee6c7d9515926ceeba37d2b6d6347ce01164b4..56dfec80e6cd9715ff3e4f8479fd6863524d70a5 100644 (file)
--- a/doc/src/sgml/trigger.sgml
+++ b/doc/src/sgml/trigger.sgml
@@ -1,5 +1,5 @@
 
 
  
@@ -431,8 +431,10 @@ typedef struct Trigger
    
 
    
-    A trigger function must return either NULL or a
-    HeapTuple pointer.  Be careful to return either
+    A trigger function must return either a
+    HeapTuple pointer or a NULL pointer
+    (not a SQL NULL, that is, do not set isNull true).
+    Be careful to return either
     tg_trigtuple or tg_newtuple,
     as appropriate, if you don't want to modify the row being operated on.