MariaDB 10.3

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select version();


version()


10.3.36-MariaDB-1:10.3.36+maria~deb10-log


BEGIN
    DECLARE finished int default 0;
    DECLARE query varchar(500) default "";
    
    DECLARE curQuery
        CURSOR FOR
            SELECT CONCAT('ALTER TABLE ',TABLE_SCHEMA ,'.', table_name, ' MODIFY COLUMN `type` tinyint(1) DEFAULT NULL NULL COMMENT "test";') 
            FROM information_schema.tables WHERE table_name = 'test_table';
        
        
    DECLARE CONTINUE HANDLER
        FOR NOT FOUND SET finished = 1;
    
    open curQuery;
    
    executeQuery: LOOP
        FETCH curQuery INTO query;
        IF finished = 1 THEN
            LEAVE executeQuery;
        END IF;
        prepare stmt from query;
        execute stmt;
    END LOOP executeQuery;
    CLOSE curQuery;
END

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 'DECLARE finished int default 0;
    DECLARE query varchar(500) default "";
  ...' at line 2


BEGIN NOT ATOMIC
    DECLARE finished int default 0;
    DECLARE query varchar(500) default "";
    
    DECLARE curQuery
        CURSOR FOR
            SELECT CONCAT('ALTER TABLE ',TABLE_SCHEMA ,'.', table_name, ' MODIFY COLUMN `type` tinyint(1) DEFAULT NULL NULL COMMENT "test";') 
            FROM information_schema.tables WHERE table_name = 'test_table';
        
        
    DECLARE CONTINUE HANDLER
        FOR NOT FOUND SET finished = 1;
    
    open curQuery;
    
    executeQuery: LOOP
        FETCH curQuery INTO query;
        IF finished = 1 THEN
            LEAVE executeQuery;
        END IF;
        prepare stmt from query;
        execute stmt;
    END LOOP executeQuery;
    CLOSE curQuery;
END