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unbounded:无界限
preceding:从分区第一行头开始,则为 unbounded。 N为:相对当前行向前的偏移量
following :与preceding相反,到该分区结束,则为 unbounded。N为:相对当前行向后的偏移量
current row:顾名思义,当前行,偏移量为0
例子:
partition by order by asc/desc rows between unbounded preceding and current row
partition by order by asc/desc rows between 1 preceding and 1 following
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