PREPARED STATEMENT in a WHILE loop - mysql

Question

I have a table autos that has a column name, I want to check first 5 rows in the table and if name value is "toyota", in table mytable write "yes", else write "no".
I write stored procedure, but mysqli_error() returns error in line, where I have EXECUTE ....
If in WHEN I write not PREPARED STATEMENT, but directly the query, the procedure works.
Please see my code and tell me, where is it wrong?
CREATE PROCEDURE proc_auto()
BEGIN
DECLARE start INT;
SET start = 0;
PREPARE stmt FROM ' SELECT name FROM autos ORDER BY id LIMIT ?,1 ';
WHILE start < 5 DO
CASE
WHEN (EXECUTE stmt USING #start ) = 'toyota'
THEN INSERT INTO mytable (log) VALUES('yes');
ELSE
INSERT INTO mytable (log) VALUES('no');
END CASE;
SET start = start + 1;
END WHILE;
END;

Answer 1

(The suggestion about EXECUTE is removed as incorrect and potentially confusing.)
The problem you are trying to solve with a stored procedure could in fact be solved without it, using an entirely different approach: just use a single INSERT ... SELECT statement instead:
INSERT INTO mytable (log)
SELECT
CASE name
WHEN 'toyota' THEN 'yes'
ELSE 'no'
END
FROM autos
ORDER BY id
LIMIT 5
That is, the above statement does the same as your stored procedure: it retrieves first 5 rows from autos and inserts 5 rows into mytable. Depending on the value of name it generates either yeses or nos.

Answer 2

Andriy M's INSERT statement is the most elegant solution, but if you still want to use a procedure, this will work:
CREATE PROCEDURE proc_auto()
BEGIN
DECLARE start INT DEFAULT 0;
PREPARE stmt FROM
'SELECT name INTO #name FROM autos ORDER BY id LIMIT ?,1';
WHILE start < 5 DO
SET #start = start;
EXECUTE stmt USING #start;
IF #name = 'toyota' THEN
INSERT INTO mytable (log) VALUES('yes');
ELSE
INSERT INTO mytable (log) VALUES('no');
END IF;
SET start = start + 1;
END WHILE;
END;
but, in this case, using a CURSOR would yield better performance:
CREATE PROCEDURE proc_auto()
BEGIN
DECLARE start INT DEFAULT 0;
DECLARE b_not_found BOOL DEFAULT FALSE;
DECLARE cur CURSOR FOR
'SELECT name FROM autos ORDER BY id LIMIT 5';
DECLARE CONTINUE HANDLER FOR NOT FOUND SET b_not_found = TRUE;
OPEN cur;
loop1: WHILE start < 5 DO
FETCH cur INTO #name;
IF b_not_found THEN
LEAVE loop1;
END IF;
IF #name = 'toyota' THEN
INSERT INTO mytable (log) VALUES('yes');
ELSE
INSERT INTO mytable (log) VALUES('no');
END IF;
SET start = start + 1;
END WHILE;
CLOSE cur;
END;