MySQL Stored Procedure inserts no data - mysql

Question

Actually I'm trying to insert some data into a table using a cursor, and I'm getting no error. It just says:
Query executed OK, 0 rows affected.
I'm trying to get data from each field of the testdatabase.wp_posts p table and insert it into an existing table `testdatabase.wp_postmeta.
My syntax is:
DROP PROCEDURE IF EXISTS add_authors_to_prod;
DELIMITER $$
CREATE PROCEDURE add_authors_to_prod()
BEGIN
DECLARE v_post_id INT;
DECLARE v_author_id INT;
DECLARE v_last_author INT DEFAULT 0;
DECLARE str VARCHAR(500);
DECLARE v_first_id INT DEFAULT 10916;
DECLARE author_csr CURSOR FOR
SELECT n.nid, p.id FROM testdatabase.wp_posts p
JOIN drupaltest.srmaif_field_data_field_auther_list auth ON auth.entity_id = p.id
JOIN drupaltest.node_field_data n ON auth.field_auther_list_nid = n.nid
ORDER BY p.id;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET v_last_author = 1;
START TRANSACTION;
OPEN author_csr;
author_loop:LOOP
FETCH author_csr INTO v_author_id, v_post_id;
IF v_last_author THEN
SET str = CONCAT(str, '}');
LEAVE author_loop;
END IF;
IF v_first_id <> v_post_id THEN
SET v_first_id = v_post_id;
SET str = CONCAT(str, '}');
INSERT INTO testdatabase.wp_postmeta (post_id, meta_key, meta_value)
VALUES(v_post_id, 'authors', CONCAT(str, v_author_id));
SET str = 'a:2:{';
ELSE
SET str = CONCAT(str,'i:', v_author_id, ';s:5:\"', v_author_id, '\";');
END IF;
END LOOP author_loop;
CLOSE author_csr;
SET v_last_author=0;
END$$
DELIMITER ;
CALL add_authors_to_prod()