将Sprite alpha颜色分量设置为值<1会对性能产生影响吗？(Does setting Sprite alpha color component to a value < 1 have a performance impact?)

SELECT 
    IF(chat.from_user=3, to_user
        , IF(chat.to_user=3, form_user, 0)) AS username,
    chat.from_user,chat.to_user,chat.message,chat.date_created 
    FROM chat 
    LEFT JOIN user fr_user ON chat.from_user = user.user_id
    LEFT JOIN user to_user ON chat.to_user = user.user_id -- since you only want to show the TO_USERNAME, you can remove above line
        WHERE (chat.from_user = 3 OR chat.to_user = 3) and chat.chat_id 
    IN
    (SELECT distinct (MAX(chat.chat_id) )
        FROM chat GROUP BY chat_group_id);

SELECT 
    IF(chat.from_user=3, to_user
        , IF(chat.to_user=3, form_user, 0)) AS username,
    chat.from_user,chat.to_user,chat.message,chat.date_created 
    FROM chat 
    LEFT JOIN user fr_user ON chat.from_user = user.user_id
    LEFT JOIN user to_user ON chat.to_user = user.user_id -- since you only want to show the TO_USERNAME, you can remove above line
        WHERE (chat.from_user = 3 OR chat.to_user = 3) and chat.chat_id 
    IN
    (SELECT distinct (MAX(chat.chat_id) )
        FROM chat GROUP BY chat_group_id);