the second-highest data value(HIGH2KEY), second-lowest data value (LOW2KEY),这两个信息在runstats中收集的,用于优化器计算Between 谓词的依据,比如满足C1 BETWEEN KEY1 AND KEY2谓词的行数,可以用下面的公式估算。KEY2 - KEY1------------------- ...
显示全部the second-highest data value(HIGH2KEY), second-lowest data value (LOW2KEY),这两个信息在runstats中收集的,用于优化器计算Between 谓词的依据,比如
满足C1 BETWEEN KEY1 AND KEY2谓词的行数,可以用下面的公式估算。
KEY2 - KEY1
------------------- x CARD
HIGH2KEY - LOW2KEY
除此之外,优化器还尝试使用范围统计信息(HIGH2KEY 和 LOW2KEY)来验证父表,方法是确保子表中的值集是父表的子集。
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