Initial RETURNING implementation

Makefile

@@ -23,7 +23,7 @@ GISTEST=nogis
 endif
 
 ifndef REGRESS
-REGRESS = extra/sqlite_fdw_post types/bitstring types/bool types/float4 types/float8 types/int4 types/int8 types/numeric types/$(GISTEST) types/macaddr types/macaddr8 types/out_of_range types/timestamp types/uuid extra/join extra/limit extra/aggregates extra/prepare extra/select_having extra/select extra/insert extra/update extra/encodings sqlite_fdw type_$(GISTEST) aggregate selectfunc 
+REGRESS = extra/sqlite_fdw_post types/bitstring types/bool types/float4 types/float8 types/int4 types/int8 types/numeric types/$(GISTEST) types/macaddr types/macaddr8 types/out_of_range types/timestamp types/uuid extra/join extra/limit extra/aggregates extra/prepare extra/select_having extra/select extra/insert extra/update extra/encodings sqlite_fdw type_$(GISTEST) aggregate selectfunc extra/returning
 endif
 
 REGRESS_OPTS = --encoding=utf8

README.md

@@ -35,13 +35,15 @@ Features
 ### Common features
 - Transactions
 - Support `INSERT`/`UPDATE`/`DELETE` (both Direct modification and Foreign modification), see [access control](#connection-to-sqlite-database-file-and-access-control) about conditions of succesfully data modification.
+- Support `RETURNING` for `INSERT`/`UPDATE`/`DELETE`.
 - Support `TRUNCATE` by deparsing into `DELETE` statement without `WHERE` clause.
 - Allow control over whether foreign servers keep connections open after transaction completion. This is controlled by `keep_connections` and defaults to on.
 - Support list cached connections to foreign servers by using function `sqlite_fdw_get_connections()`
 - Support discard cached connections to foreign servers by using function `sqlite_fdw_disconnect()`, `sqlite_fdw_disconnect_all()`.
 - Support Bulk `INSERT` by using `batch_size` option
 - Support `INSERT`/`UPDATE` with generated column
-- Support `ON CONFLICT DO NOTHING`
+- Support `INSERT` ... `ON CONFLICT DO NOTHING`
+- Support `WITH CHECK OPTION` views after a foreign table
 - Support mixed SQLite [data affinity](https://www.sqlite.org/datatype3.html) input and filtering (`SELECT`/`WHERE` usage) for such data types as
 	- `timestamp`: `text` and `int`,
 	- `uuid`: `text`(32..39) and `blob`(16),
@@ -59,7 +61,8 @@ Features
 
 ### Pushing down
 - `WHERE` clauses are pushdowned
-- Aggregate function are pushdowned
+- `RETURNING` clauses are pushdowned
+- Some aggregate functions are pushdowned
 - `ORDER BY` is pushdowned
 - Joins (left/right/inner/cross/semi) are pushdowned
 - `CASE` expressions are pushdowned.
@@ -700,6 +703,13 @@ funct_name (type arg ...)
 	}
 }
 ```
+
+To debug, you need to build PostgreSQL in debug mode. Use the following options.
+```bash
+./configure --prefix=<path_to_postgresql_build_folder> --enable-cassert --enable-debug CFLAGS="-ggdb -O0 -g3 -fno-omit-frame-pointer"
+```
+Also please refer https://wiki.postgresql.org/wiki/Developer_FAQ#What_debugging_features_are_available.3F
+
 Useful links
 ------------
 

connection.c

@@ -184,6 +184,7 @@ sqlite_get_connection(ForeignServer *server, bool truncatable)
 }
 
 /*
+ * sqlite_open_db
  * Open remote sqlite database using specified database path
  * and flags of opened file descriptor mode.
  */
@@ -230,7 +231,7 @@ sqlite_make_new_connection(ConnCacheEntry *entry, ForeignServer *server)
 {
 	const char *dbpath = NULL;
 	ListCell   *lc;
-	int flags = 0;
+	int			flags = 0;
 
 	Assert(entry->conn == NULL);
 
@@ -389,8 +390,8 @@ sqlite_begin_remote_xact(ConnCacheEntry *entry)
 	}
 }
 
-
 /*
+ * sqlitefdw_report_error
  * Report an sqlite execution error
  */
 void
@@ -400,7 +401,7 @@ sqlitefdw_report_error(int elevel, sqlite3_stmt * stmt, sqlite3 * conn,
 	const char *message = sqlite3_errmsg(conn);
 	int			sqlstate = ERRCODE_FDW_ERROR;
 
-	/* copy sql before callling another SQLite API */
+	/* copy sql before calling another SQLite API */
 	if (message)
 		message = pstrdup(message);
 
@@ -418,9 +419,9 @@ sqlitefdw_report_error(int elevel, sqlite3_stmt * stmt, sqlite3 * conn,
 			));
 }
 
-
 /*
- * sqlitefdw_xact_callback --- cleanup at main-transaction end.
+ * sqlitefdw_xact_callback
+ * cleanup at main-transaction end.
  */
 static void
 sqlitefdw_xact_callback(XactEvent event, void *arg)
@@ -1038,7 +1039,7 @@ sqlite_cache_stmt(ForeignServer *server, sqlite3_stmt * *stmt)
 }
 
 /*
- * finalize all sqlite statement
+ * finalize all SQLite statement
  */
 static void
 sqlite_finalize_list_stmt(List **list)