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继上一篇提到的UNION/UNION ALL会影响执行计划,再次碰到一个类似的问题.一个SQL加了DISTINCT跟不加DISTINCT的执行计划完全不同,导致执行时间差了好多倍. 原始的SQL如下所示, (注意DISTINCT) 执行计划如下所示, 这个执行计划最耗时的一步是"BUFFER SORT"执行了6982次.当然这个跟View - V_TEMP_口口_PROP_HIST 有一定关系.不过要知道 IN 子查询的结果集最多是1,因为用了ROWNUM=1. (其实在这个例子中结果…
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