Allow MOVE FORWARD n, MOVE BACKWARD n, MOVE FORWARD ALL, MOVE BACKWARD ALL

in plpgsql.  Clean up a couple of corner cases in the MOVE/FETCH syntax.

Pavel Stehule

Author: tglsfdc

doc/src/sgml/plpgsql.sgml

@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.142 2009/06/18 10:22:08 petere Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.143 2009/09/29 20:05:29 tgl Exp $ -->
 
 <chapter id="plpgsql">
   <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -2655,16 +2655,18 @@ MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <
     </para>
 
     <para>
-     The options for the <replaceable>direction</replaceable> clause are
-     the same as for <command>FETCH</>, namely
+     The <replaceable>direction</replaceable> clause can be any of the
+     variants allowed in the SQL <xref linkend="sql-fetch"
+     endterm="sql-fetch-title"> command, namely
      <literal>NEXT</>,
      <literal>PRIOR</>,
      <literal>FIRST</>,
      <literal>LAST</>,
      <literal>ABSOLUTE</> <replaceable>count</replaceable>,
      <literal>RELATIVE</> <replaceable>count</replaceable>,
-     <literal>FORWARD</>, or
-     <literal>BACKWARD</>.
+     <literal>ALL</>,
+     <literal>FORWARD</> <optional> <replaceable>count</replaceable> | <literal>ALL</> </optional>, or
+     <literal>BACKWARD</> <optional> <replaceable>count</replaceable> | <literal>ALL</> </optional>.
      Omitting <replaceable>direction</replaceable> is the same
      as specifying <literal>NEXT</>.
      <replaceable>direction</replaceable> values that require moving
@@ -2678,6 +2680,7 @@ MOVE <optional> <replaceable>direction</replaceable> { FROM | IN } </optional> <
 MOVE curs1;
 MOVE LAST FROM curs3;
 MOVE RELATIVE -2 FROM curs4;
+MOVE FORWARD 2 FROM curs4;
 </programlisting>
        </para>
      </sect3>

src/pl/plpgsql/src/gram.y

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.127 2009/07/22 02:31:38 joe Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/gram.y,v 1.128 2009/09/29 20:05:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,6 +48,8 @@ static	PLpgSQL_expr	*read_sql_stmt(const char *sqlstart);
 static	PLpgSQL_type	*read_datatype(int tok);
 static	PLpgSQL_stmt	*make_execsql_stmt(const char *sqlstart, int lineno);
 static	PLpgSQL_stmt_fetch *read_fetch_direction(void);
+static	void			 complete_direction(PLpgSQL_stmt_fetch *fetch,
+											bool *check_FROM);
 static	PLpgSQL_stmt	*make_return_stmt(int lineno);
 static	PLpgSQL_stmt	*make_return_next_stmt(int lineno);
 static	PLpgSQL_stmt	*make_return_query_stmt(int lineno);
@@ -178,6 +180,7 @@ static List				*read_raise_options(void);
 		 * Keyword tokens
 		 */
 %token	K_ALIAS
+%token	K_ALL
 %token	K_ASSIGN
 %token	K_BEGIN
 %token	K_BY
@@ -1622,6 +1625,15 @@ stmt_fetch		: K_FETCH lno opt_fetch_direction cursor_variable K_INTO
 						if (yylex() != ';')
 							yyerror("syntax error");
 
+						/*
+						 * We don't allow multiple rows in PL/pgSQL's FETCH
+						 * statement, only in MOVE.
+						 */
+						if (fetch->returns_multiple_rows)
+							ereport(ERROR,
+									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+									 errmsg("FETCH statement cannot return multiple rows")));
+
 						fetch->lineno = $2;
 						fetch->rec		= rec;
 						fetch->row		= row;
@@ -2252,6 +2264,9 @@ make_execsql_stmt(const char *sqlstart, int lineno)
 }
 
 
+/*
+ * Read FETCH or MOVE direction clause (everything through FROM/IN).
+ */
 static PLpgSQL_stmt_fetch *
 read_fetch_direction(void)
 {
@@ -2269,6 +2284,7 @@ read_fetch_direction(void)
 	fetch->direction = FETCH_FORWARD;
 	fetch->how_many  = 1;
 	fetch->expr      = NULL;
+	fetch->returns_multiple_rows = false;
 
 	/*
 	 * Most of the direction keywords are not plpgsql keywords, so we
@@ -2311,26 +2327,46 @@ read_fetch_direction(void)
 										   NULL);
 		check_FROM = false;
 	}
+	else if (pg_strcasecmp(yytext, "all") == 0)
+	{
+		fetch->how_many = FETCH_ALL;
+		fetch->returns_multiple_rows = true;
+	}
 	else if (pg_strcasecmp(yytext, "forward") == 0)
 	{
-		/* use defaults */
+		complete_direction(fetch, &check_FROM);
 	}
 	else if (pg_strcasecmp(yytext, "backward") == 0)
 	{
 		fetch->direction = FETCH_BACKWARD;
+		complete_direction(fetch, &check_FROM);
 	}
-	else if (tok != T_SCALAR)
+	else if (tok == K_FROM || tok == K_IN)
 	{
+		/* empty direction */
+		check_FROM = false;
+	}
+	else if (tok == T_SCALAR)
+	{
+		/* Assume there's no direction clause and tok is a cursor name */
 		plpgsql_push_back_token(tok);
-		fetch->expr = read_sql_expression2(K_FROM, K_IN,
-										   "FROM or IN",
-										   NULL);
 		check_FROM = false;
 	}
 	else
 	{
-		/* Assume there's no direction clause */
+		/*
+		 * Assume it's a count expression with no preceding keyword.
+		 * Note: we allow this syntax because core SQL does, but we don't
+		 * document it because of the ambiguity with the omitted-direction
+		 * case.  For instance, "MOVE n IN c" will fail if n is a scalar.
+		 * Perhaps this can be improved someday, but it's hardly worth a
+		 * lot of work.
+		 */
 		plpgsql_push_back_token(tok);
+		fetch->expr = read_sql_expression2(K_FROM, K_IN,
+										   "FROM or IN",
+										   NULL);
+		fetch->returns_multiple_rows = true;
 		check_FROM = false;
 	}
 
@@ -2345,6 +2381,43 @@ read_fetch_direction(void)
 	return fetch;
 }
 
+/*
+ * Process remainder of FETCH/MOVE direction after FORWARD or BACKWARD.
+ * Allows these cases:
+ *   FORWARD expr,  FORWARD ALL,  FORWARD
+ *   BACKWARD expr, BACKWARD ALL, BACKWARD
+ */
+static void
+complete_direction(PLpgSQL_stmt_fetch *fetch,  bool *check_FROM)
+{
+	int			tok;
+
+	tok = yylex();
+	if (tok == 0)
+		yyerror("unexpected end of function definition");
+
+	if (tok == K_FROM || tok == K_IN)
+	{
+		*check_FROM = false;
+		return;
+	}
+
+	if (tok == K_ALL)
+	{
+		fetch->how_many = FETCH_ALL;
+		fetch->returns_multiple_rows = true;
+		*check_FROM = true;
+		return;
+	}
+
+	plpgsql_push_back_token(tok);
+	fetch->expr = read_sql_expression2(K_FROM, K_IN,
+									   "FROM or IN",
+									   NULL);
+	fetch->returns_multiple_rows = true;
+	*check_FROM = false;
+}
+
 
 static PLpgSQL_stmt *
 make_return_stmt(int lineno)
@@ -3043,11 +3116,11 @@ make_case(int lineno, PLpgSQL_expr *t_expr,
 
 			/* copy expression query without SELECT keyword (expr->query + 7) */
 			Assert(strncmp(expr->query, "SELECT ", 7) == 0);
-			
+
 			/* And do the string hacking */
 			initStringInfo(&ds);
 
-			appendStringInfo(&ds, "SELECT $%d IN(%s)", 
+			appendStringInfo(&ds, "SELECT $%d IN(%s)",
 								nparams + 1,
 								expr->query + 7);
 

src/pl/plpgsql/src/pl_funcs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.80 2009/07/22 02:31:38 joe Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.81 2009/09/29 20:05:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -854,7 +854,7 @@ dump_cursor_direction(PLpgSQL_stmt_fetch *stmt)
 		printf("\n");
 	}
 	else
-		printf("%d\n", stmt->how_many);
+		printf("%ld\n", stmt->how_many);
 
 	dump_indent -= 2;
 }

src/pl/plpgsql/src/plpgsql.h

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.116 2009/09/22 23:43:42 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.117 2009/09/29 20:05:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -517,9 +517,10 @@ typedef struct
 	PLpgSQL_row *row;
 	int			curvar;			/* cursor variable to fetch from */
 	FetchDirection direction;	/* fetch direction */
-	int			how_many;		/* count, if constant (expr is NULL) */
+	long		how_many;		/* count, if constant (expr is NULL) */
 	PLpgSQL_expr *expr;			/* count, if expression */
 	bool		is_move;		/* is this a fetch or move? */
+	bool		returns_multiple_rows;	/* can return more than one row? */
 } PLpgSQL_stmt_fetch;
 
 

src/pl/plpgsql/src/scan.l

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.71 2009/07/13 00:42:18 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.72 2009/09/29 20:05:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -147,6 +147,7 @@ param			\${digit}+
 =				{ return K_ASSIGN;			}
 \.\.			{ return K_DOTDOT;			}
 alias			{ return K_ALIAS;			}
+all				{ return K_ALL;				}
 begin			{ return K_BEGIN;			}
 by				{ return K_BY;   			}
 case			{ return K_CASE;			}

src/test/regress/expected/plpgsql.out

@@ -3025,6 +3025,28 @@ select * from sc_test();
            0
 (3 rows)
 
+create or replace function sc_test() returns setof integer as $$
+declare
+  c refcursor;
+  x integer;
+begin
+  open c scroll for execute 'select f1 from int4_tbl';
+  fetch last from c into x;
+  while found loop
+    return next x;
+    move backward 2 from c;
+    fetch relative -1 from c into x;
+  end loop;
+  close c;
+end;
+$$ language plpgsql;
+select * from sc_test();
+   sc_test   
+-------------
+ -2147483647
+      123456
+(2 rows)
+
 create or replace function sc_test() returns setof integer as $$
 declare
   c cursor for select * from generate_series(1, 10);
@@ -3052,6 +3074,26 @@ select * from sc_test();
        9
 (3 rows)
 
+create or replace function sc_test() returns setof integer as $$
+declare
+  c cursor for select * from generate_series(1, 10);
+  x integer;
+begin
+  open c;
+  move forward all in c;
+  fetch backward from c into x;
+  if found then
+    return next x;
+  end if;
+  close c;
+end;
+$$ language plpgsql;
+select * from sc_test();
+ sc_test 
+---------
+      10
+(1 row)
+
 drop function sc_test();
 -- test qualified variable names
 create function pl_qual_names (param1 int) returns void as $$
@@ -3864,7 +3906,7 @@ drop function strtest();
 -- Test anonymous code blocks.
 DO $$
 DECLARE r record;
-BEGIN 
+BEGIN
     FOR r IN SELECT rtrim(roomno) AS roomno, comment FROM Room ORDER BY roomno
     LOOP
         RAISE NOTICE '%, %', r.roomno, r.comment;
@@ -3887,7 +3929,7 @@ LINE 1: DO LANGUAGE plpgsql $$begin return 1; end$$;
                                            ^
 DO LANGUAGE plpgsql $$
 DECLARE r record;
-BEGIN 
+BEGIN
     FOR r IN SELECT rtrim(roomno) AS roomno, foo FROM Room ORDER BY roomno
     LOOP
         RAISE NOTICE '%, %', r.roomno, r.comment;