Document that age() adds days, then full months.

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 387c4e81c8fc65896fd62f784f701a981c0f3dba..5d5a86a0c7fa066b2ddc1c9b141f3da155fb285a 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -1,4 +1,4 @@
-
+
 
  
   Functions and Operators
@@ -5895,6 +5895,17 @@ SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
    CST7CDT.
   
 
+  
+   Note that when the age function operates on multi-month
+   intervals, PostgreSQL adds days to the earlier date
+   until full months can be added.  This yields a different result than
+   adding full months first if the interval crosses from one month to the
+   next.  For example, age('2004-06-01', '2004-04-30') yeilds
+   1 mon 1 day using the PostgreSQL method,
+   while adding the month first would yield 1 mon 2 days
+   because May has 31 days, while April has only 30.
+  
+
   
    <function>EXTRACT</function>, <function>date_part</function>