CREATE
    DEFINER = root@localhost procedure prepare_data()
BEGIN
    DECLARE i INT DEFAULT 1;
    DECLARE emailString CHAR(16) DEFAULT 'test';
    DECLARE readyEmailString CHAR(32);

    WHILE i < 100
        DO
            SET readyEmailString = CONCAT(emailString, CAST(i AS CHAR(16)), '@test.de');
            INSERT INTO webshop.user(is_active, name, lower_name, email)
            VALUES ('1', 'harry', 'potter', readyEmailString);
            SET i = i + 1;
        END WHILE;
END;