CSV NULL Documentation

Update docs to clearly explain NULL value matching behavior, per Andrew.

Backpatch to 8.4.X.

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index ff91ee2d9f75f191bbb9904942d80df889e58ee3..79ed7c204e3e0710729dcfe02afee73a41506b2c 100644 (file)
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -1,5 +1,5 @@
 
 
@@ -550,10 +550,13 @@ COPY count
    
     The CSV format has no standard way to distinguish a
     NULL value from an empty string.
-    PostgreSQL's COPY handles this using
-    quoting. A NULL is output as an empty string without
-    quotes, while an empty string data value is double-quoted
-    ("").  Reading values follows similar rules. You can
+    PostgreSQL's COPY handles this by
+    quoting. A NULL is output as the NULL
+    parameter and is not quoted, while a non-NULL value matching the
+    the NULL parameter string is quoted. Therefore, using the default
+    settings, a NULL is written as an unquoted empty
+    string, while an empty string data value is written with double quotes
+    (""). Reading values follows similar rules. You can
     use FORCE NOT NULL to prevent NULL input
     comparisons for specific columns.