MySQL - UPDATE in batches using WHILE DO - mysql

Question

Can someone give me pointers on what I'm doing wrong here?
I keep getting You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near...
I'm trying to run an UPDATE command in small batches to prevent the table from being blocked (while running through 10 million records).
DELIMITER //
CREATE FUNCTION batch_update()
BEGIN
SET processed = 0;
SET eachbatch = 1000;
WHILE processed < 1000000 DO
UPDATE `users` SET `active` = 1 WHERE `active` = 0 LIMIT eachbatch;
-- Finish when no rows remaining
IF ROW_COUNT() = 0 THEN LEAVE;
END IF;
-- No infinite loop, thanks
SET processed = processed + eachbatch;
END WHILE;
END //
DELIMITER ;
CALL batch_update();
Edit: For anyone that needs a pointer, I got it working like this:
DROP FUNCTION IF EXISTS process_batch_rows;
DELIMITER //
CREATE FUNCTION process_batch_rows() RETURNS VARCHAR(10) DETERMINISTIC
BEGIN
DECLARE processed INT DEFAULT 0;
DECLARE eachbatch INT DEFAULT 1000;
my_loop: WHILE processed < 1000000
DO
UPDATE `users` SET `active` = 1 WHERE `active` = 0 LIMIT eachbatch;
IF ROW_COUNT() < 1 THEN
LEAVE my_loop;
END IF;
SET processed = processed + eachbatch;
END WHILE my_loop;
RETURN "Done";
END //
DELIMITER ;
SELECT process_batch_rows();

Answer 1

Try This one I have added comments wherever needed =>
DELIMITER //
-- You must specify return type
CREATE FUNCTION batch_update() RETURNS VARCHAR(10) DETERMINISTIC
BEGIN
-- you must declare variables
DECLARE processed int(10);
DECLARE eachbatch int(10);
SET processed = 0;
SET eachbatch = 1000;
-- needed my loop here so it can be used in leave
myloop: WHILE processed < 1000000 DO
UPDATE `users` SET `active` = 1 WHERE `active` = 0 LIMIT eachbatch;
-- Finish when no rows remaining
IF ROW_COUNT() = 0
THEN
LEAVE myloop;
END IF;
-- No infinite loop, thanks
SET processed = processed + eachbatch;
END WHILE;
return 'Done';
END //
DELIMITER ;