MariaDB 10.3

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CREATE TABLE TEST1 (ID int);
CREATE TABLE TEST2 (ID int);
DELIMITER $$

SELECT 
   @query = @query + CONCAT('GRANT SELECT ON drupal.', TABLE_NAME, ' to ''test'';') As queryStrings 
FROM 
    INFORMATION_SCHEMA.TABLES 
WHERE 
    TABLE_SCHEMA LIKE 'fiddle_%' AND TABLE_NAME LIKE 'TEST%';
    
PREPARE stmt FROM @query;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

$$
DELIMITER ;
You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'DELIMITER $$

SELECT 
   @query = @query + CONCAT('GRANT SELECT ON drupal.', TAB' at line 1