docs: clarify handling of column lists in COPY TO/FROM

Previously it was unclear how COPY FROM handled cases where not all
columns were specified, or if the order didn't match.

Reported-by: [email protected]
Discussion: https://postgr.es/m/157487729344.7213.14245726713444755296@wrigleys.postgresql.org

Backpatch-through: 9.4

diff --git a/doc/src/sgml/ref/copy.sgml b/doc/src/sgml/ref/copy.sgml
index d9b7c4d0d488dde8b8c60e5349ae47e1ad2027eb..a99f8155e465c7dfa87f2dca0f6fd2a00a27333d 100644 (file)
--- a/doc/src/sgml/ref/copy.sgml
+++ b/doc/src/sgml/ref/copy.sgml
@@ -61,11 +61,11 @@ COPY { table_name [ ( 
   
 
   
-   If a list of columns is specified, COPY will
-   only copy the data in the specified columns to or from the file.
-   If there are any columns in the table that are not in the column list,
-   COPY FROM will insert the default values for
-   those columns.
+   If a column list is specified, COPY TO copies only
+   the data in the specified columns to the file.  For COPY
+   FROM, each field in the file is inserted, in order, into the
+   specified column.  Table columns not specified in the COPY
+   FROM column list will receive their default values.