Here's a mysql stored procedure to loop through the results of a select query that returns ids and performs an additional operation on each id.

mysql_procedure_loop_ids_and_insert.sql

DROP PROCEDURE IF EXISTS migrateById;
DELIMITER $$

CREATE PROCEDURE migrateById()
BEGIN
  DECLARE done INT DEFAULT FALSE;
  DECLARE _post_id INT;
  DECLARE migrate_ids CURSOR FOR 
  
  # modify the select statement to returns IDs, which will be assigned the variable `_post_id`
  # the following statement gets all wp attachments that are missing attachment metadata
  SELECT DISTINCT ID FROM wp_posts WHERE post_type = "attachment" AND ID NOT IN ( SELECT post_id FROM wp_postmeta WHERE meta_key = "_wp_attachment_metadata" AND meta_value IS NOT NULL);
  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=TRUE;

  OPEN migrate_ids;

  read_loop: LOOP
    FETCH migrate_ids INTO _post_id;

    IF done THEN
      LEAVE read_loop;
    END IF;

    # modify the insert statement to perform your operation with the `_post_id` 
    # the following insert statement adds missing metadata in wordpress
    INSERT INTO `wp_postmeta` (`post_id`, `meta_key`, `meta_value`)
    VALUES
    (_post_id, 'mapped_key', 'mapped_value');

    SET done=FALSE;
  END LOOP;

  CLOSE migrate_ids;
END; $$

CALL migrateById();