Only evaluate default values as required when doing COPY FROM

adunstan · adunstan · commit 276393f53efb · 2023-10-01T10:18:41.000-04:00
Commit 9f8377f was a little too eager in fetching default values. Normally this would not matter, but if the default value is not valid for the type (e.g. a varchar that's too long) it caused an unnecessary error. Complaint and fix from Laurenz Albe Backpatch to release 16. Discussion: https://postgr.es/m/75a7b7483aeb331aa017328d606d568fc715b90d.camel@cybertec.at
diff --git a/src/backend/commands/copyfrom.c b/src/backend/commands/copyfrom.c
@@ -1571,7 +1571,14 @@ BeginCopyFrom(ParseState *pstate,
 		/* Get default info if available */
 		defexprs[attnum - 1] = NULL;
 
-		if (!att->attgenerated)
+		/*
+		 * We only need the default values for columns that do not appear in
+		 * the column list, unless the DEFAULT option was given. We never need
+		 * default values for generated columns.
+		 */
+		if ((cstate->opts.default_print != NULL ||
+			 !list_member_int(cstate->attnumlist, attnum)) &&
+			!att->attgenerated)
 		{
 			Expr	   *defexpr = (Expr *) build_column_default(cstate->rel,
 																attnum);
diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out
@@ -240,3 +240,20 @@ SELECT * FROM header_copytest ORDER BY a;
 (5 rows)
 
 drop table header_copytest;
+-- test COPY with overlong column defaults
+create temp table oversized_column_default (
+    col1 varchar(5) DEFAULT 'more than 5 chars',
+    col2 varchar(5));
+-- normal COPY should work
+copy oversized_column_default from stdin;
+-- error if the column is excluded
+copy oversized_column_default (col2) from stdin;
+ERROR:  value too long for type character varying(5)
+\.
+invalid command \.
+-- error if the DEFAULT option is given
+copy oversized_column_default from stdin (default '');
+ERROR:  value too long for type character varying(5)
+\.
+invalid command \.
+drop table oversized_column_default;
diff --git a/src/test/regress/sql/copy.sql b/src/test/regress/sql/copy.sql
@@ -268,3 +268,18 @@ a	c	b
 
 SELECT * FROM header_copytest ORDER BY a;
 drop table header_copytest;
+
+-- test COPY with overlong column defaults
+create temp table oversized_column_default (
+    col1 varchar(5) DEFAULT 'more than 5 chars',
+    col2 varchar(5));
+-- normal COPY should work
+copy oversized_column_default from stdin;
+\.
+-- error if the column is excluded
+copy oversized_column_default (col2) from stdin;
+\.
+-- error if the DEFAULT option is given
+copy oversized_column_default from stdin (default '');
+\.
+drop table oversized_column_default;
