为了实现执行计划管理，优化器会为所有执行次数超过一次的SQL语句维护该SQL语句的每个执行计划的历史列表（plan history）。优化器通过维护一个语句执行的日志条目（statement log）来识别该SQL语句是否为第二次执行。
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Sheng Jing took our country ancient times in the capital city plan construction history the last model, also has enormously enriched the Chinese capital city plan history treasure house.
盛京作为我国古代都城规划建设史上最后一个范例，也极大地丰富了中国都城规划史的宝库。
Greg Behrman's book is the first comprehensive history of the Marshall Plan since the end of the cold war.
格雷戈·贝尔曼的这本书是自冷战结束以来首部全面的介绍马歇尔计划的历史。
History does not relate, though Hepburn later admitted that her original plan that morning in 1967 had been to follow the hearse, then slip quietly into the church and sit at the back.
历史没有记载，不过赫本后来承认1967年的那个早上自己原本计划跟随灵车，然后静悄悄的走进教堂，坐在后排的位置。
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