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                當隔離級別設置為Repeatable read 時,可以避免不可重復讀。當singo拿著工資卡去消費時,一旦系統開始讀取工資卡信息(即事務開始),singo的老婆就不可能對該記錄進行修改,也就是singo的老婆不能在此時轉賬。 雖然Repeatable read避免了不可重復讀,但還有可能出現幻讀 。 singo的老婆工作在銀行部門,她時常通過銀行內部系統查看singo的信用卡消費記錄。有一天,她正在查詢到singo當月信用卡的總消費金額 (select sum(amount) from transaction where month = 本月)為80元,而singo此時正好在外面胡吃海塞后在收銀臺買單,消費1000元,即新增了一條1000元的消費記錄(insert transaction ... ),并提交了事務,隨后singo的老婆將singo當月信用卡消費的明細打印到A4紙上,卻發現消費總額為1080元,singo的老婆很詫異,以為出 現了幻覺,幻讀就這樣產生了。 注:Mysql的默認隔離級別就是Repeatable read
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