Postgresql游标编译过程和编译结果

drop table tf1;
create table tf1(c1 int, c2 int,  c3 varchar(32), c4 varchar(32), c5 int);
insert into tf1 values(1,1000, 'China','Dalian', 23000);
insert into tf1 values(2,4000, 'Janpan', 'Tokio', 45000);
insert into tf1 values(3,1500, 'China', 'Xian', 25000);
insert into tf1 values(4,300, 'China', 'Changsha', 24000);
insert into tf1 values(5,400,'USA','New York', 35000);
insert into tf1 values(6,5000, 'USA', 'Bostom', 15000);

CREATE  OR REPLACE FUNCTION tfun1() RETURNS int AS $$
DECLARE
    curs1 refcursor;                       
    curs2 CURSOR FOR SELECT c1 FROM tf1;
    curs3 CURSOR (key integer) FOR SELECT * FROM tf1 WHERE c1 > key;
    
    x int;
    y tf1%ROWTYPE;
BEGIN
    open curs1 FOR SELECT * FROM tf1 WHERE c1 > 3;
    fetch curs1 into y; RAISE NOTICE 'curs1 : %', y.c3;
    fetch curs1 into y; RAISE NOTICE 'curs1 : %', y.c3;

    open curs2;
    fetch curs2 into x; RAISE NOTICE 'curs2 : %', x;
    fetch curs2 into x; RAISE NOTICE 'curs2 : %', x;
    
    OPEN curs3(4);  -- OPEN curs3(key := 4);
    fetch curs3 into y; RAISE NOTICE 'curs3 : %', y.c4;
    fetch curs3 into y; RAISE NOTICE 'curs3 : %', y.c4;
    return 0;
END;
$$ LANGUAGE plpgsql;

select tfun1();

decl_statement	: decl_varname decl_const decl_datatype decl_collate decl_notnull decl_defval
					{
						PLpgSQL_variable	*var;

						/*
						 * If a collation is supplied, insert it into the
						 * datatype.  We assume decl_datatype always returns
						 * a freshly built struct not shared with other
						 * variables.
						 */
						if (OidIsValid($4))
						{
							if (!OidIsValid($3->collation))
								ereport(ERROR,
										(errcode(ERRCODE_DATATYPE_MISMATCH),
										 errmsg("collations are not supported by type %s",
												format_type_be($3->typoid)),
										 parser_errposition(@4)));
							$3->collation = $4;
						}

						var = plpgsql_build_variable($1.name, $1.lineno,
													 $3, true);
						var->isconst = $2;
						var->notnull = $5;
						var->default_val = $6;

						/*
						 * The combination of NOT NULL without an initializer
						 * can't work, so let's reject it at compile time.
						 */
						if (var->notnull && var->default_val == NULL)
							ereport(ERROR,
									(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
									 errmsg("variable \"%s\" must have a default value, since it's declared NOT NULL",
											var->refname),
									 parser_errposition(@5)));
					}
				| decl_varname K_ALIAS K_FOR decl_aliasitem ';'
					{
						plpgsql_ns_additem($4->itemtype,
										   $4->itemno, $1.name);
					}
				| decl_varname opt_scrollable K_CURSOR
					{ plpgsql_ns_push($1.name, PLPGSQL_LABEL_OTHER); }
				  decl_cursor_args decl_is_for decl_cursor_query
					{
						PLpgSQL_var *new;
						PLpgSQL_expr *curname_def;
						char		buf[NAMEDATALEN * 2 + 64];
						char		*cp1;
						char		*cp2;

						/* pop local namespace for cursor args */
						plpgsql_ns_pop();

						new = (PLpgSQL_var *)
							plpgsql_build_variable($1.name, $1.lineno,
												   plpgsql_build_datatype(REFCURSOROID,
																		  -1,
																		  InvalidOid,
																		  NULL),
												   true);

						curname_def = palloc0(sizeof(PLpgSQL_expr));

						/* Note: refname has been truncated to NAMEDATALEN */
						cp1 = new->refname;
						cp2 = buf;
						/*
						 * Don't trust standard_conforming_strings here;
						 * it might change before we use the string.
						 */
						if (strchr(cp1, '\\') != NULL)
							*cp2++ = ESCAPE_STRING_SYNTAX;
						*cp2++ = '\'';
						while (*cp1)
						{
							if (SQL_STR_DOUBLE(*cp1, true))
								*cp2++ = *cp1;
							*cp2++ = *cp1++;
						}
						strcpy(cp2, "'::pg_catalog.refcursor");
						curname_def->query = pstrdup(buf);
						curname_def->parseMode = RAW_PARSE_PLPGSQL_EXPR;
						new->default_val = curname_def;

						new->cursor_explicit_expr = $7;
						if ($5 == NULL)
							new->cursor_explicit_argrow = -1;
						else
							new->cursor_explicit_argrow = $5->dno;
						new->cursor_options = CURSOR_OPT_FAST_PLAN | $2;
					}
				;

#define CURSOR_OPT_BINARY		0x0001	/* BINARY */
#define CURSOR_OPT_SCROLL		0x0002	/* SCROLL explicitly given */
#define CURSOR_OPT_NO_SCROLL	0x0004	/* NO SCROLL explicitly given */
#define CURSOR_OPT_INSENSITIVE	0x0008	/* INSENSITIVE */
#define CURSOR_OPT_ASENSITIVE	0x0010	/* ASENSITIVE */
#define CURSOR_OPT_HOLD			0x0020	/* WITH HOLD */
/* these planner-control flags do not correspond to any SQL grammar: */
#define CURSOR_OPT_FAST_PLAN	0x0100	/* prefer fast-start plan */
#define CURSOR_OPT_GENERIC_PLAN 0x0200	/* force use of generic plan */
#define CURSOR_OPT_CUSTOM_PLAN	0x0400	/* force use of custom plan */
#define CURSOR_OPT_PARALLEL_OK	0x0800	/* parallel mode OK */