don't overwrite col mappings

testing/insert.test

@@ -865,3 +865,11 @@ do_execsql_test_in_memory_any_error wrong-column-count-partial-columns-values-to
     CREATE TABLE t(a, b, c);
     INSERT INTO t(a) VALUES (1, 2);
 }
+
+
+# https://github.com/tursodatabase/turso/issues/3951
+do_execsql_test_on_specific_db 1 {:memory:} insert-999999999  {
+create table t(a);
+insert into t(a, a) values (2, 3);
+select * from t;
+}{2}