MySQL: Passing procedure params to EXECUTE USING statement - mysql

Question

This is MySQL 5.1.
(Note: I realize there are better ways of doing this particular example, this is not my real code)
Here is what I want to do:
The below procedure gets created, but when I CALL it, I get "ERROR 1210 (HY000): Incorrect arguments to EXECUTE"
DELIMITER //
CREATE PROCEDURE get_users_by_state(IN state CHAR(2))
READS SQL DATA
BEGIN
SET #mystate = state;
SET #sql = CONCAT('SELECT * FROM test_table WHERE state = "?"');
PREPARE stmt FROM #sql;
EXECUTE stmt USING #mystate;
END;
//
CALL get_users_by_state('AA')//
ERROR 1210 (HY000): Incorrect arguments to EXECUTE
Is there a way to pass the procedure's parameters to the EXECUTE USING statement?
Here is a version that does indeed work, but irks me:
CREATE PROCEDURE get_users_by_state(IN state CHAR(2))
READS SQL DATA
BEGIN
SET #sql = CONCAT('SELECT * FROM test_table WHERE state = "', state, '"')
PREPARE stmt FROM #sql;
EXECUTE stmt;
END;
//
As a side-question, does MySQL have any facilities for escaping strings, like Postgres' quote_literal() and quote_ident()?
For a point of reference, here's something somewhat equivalent for Postgres:
CREATE OR REPLACE FUNCTION get_info_by_state(character)
RETURNS SETOF ret_type AS
$BODY$
DECLARE
sql text;
BEGIN
sql := 'SELECT uid, some_data FROM test_table WHERE state = ' || quote_literal($1);
RETURN QUERY EXECUTE sql;
END
$BODY$
LANGUAGE 'plpgsql' VOLATILE
Thanks!

Answer 1

I don't think you need double quotes around the parameter holder.
Update Here, lest there be no misunderstanding:
DELIMITER //
CREATE PROCEDURE get_users_by_state(IN state CHAR(2))
READS SQL DATA
BEGIN
SET #mystate = state;
SET #sql = CONCAT('SELECT * FROM test_table WHERE state = ?');
PREPARE stmt FROM #sql;
EXECUTE stmt USING #mystate;
END;
//