over 疑问

over(order by salary range between 50 preceding and 150 following)每行对应的数据窗口是之前行幅度值不超过50，之后行幅度值不超过150的数据记录
over(order by salary rows between 50 perceding and 150 following)前50行，后150行
over（order by salary rows between unbounded preceding and unbounded following）所有行
over（order by salary range between unbounded preceding and unbounded following）所有行

上面的between后面的参数是上面意思，不能理解~数据窗口？？

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