Add note that COALESCE and NULLIF are shorthand forms of CASE.

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 5b3012625ea2a4d101dc27c6a9140ecf6099781d..48bdb2a5e1cf19014f0819d25b3f22b6b8387b30 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1,4 +1,4 @@
-
+
 
 
  Functions and Operators
@@ -2618,6 +2618,19 @@ SELECT COALESCE(description, short_description, '(none)') ...
 SELECT NULLIF(value, '(none)') ...
 
   
+
+  
+   
+    COALESCE and NULLIF are
+    just shorthand for CASE expressions.  They are actually
+    converted into CASE expressions at a very early stage
+    of processing, and subsequent processing thinks it is dealing with
+    CASE.  Thus an incorrect COALESCE or
+    NULLIF usage may draw an error message that
+    refers to CASE.
+   
+  
+