Mysql窗口函数

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函数名(字段名) over(子句)

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函数名(字段名) over(partition by order by rows between )

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rows between 2 preceding and current row # 取本行和前面两行

rows between unbounded preceding and current row # 取本行和之前所有的行

rows between current row and unbounded following # 取本行和之后所有的行

rows between 3 preceding and 1 following # 从前面三行和下面一行，总共五行

# 当order by后面没有rows between时，窗口规范默认是取本行和之前所有的行

# 当order by和rows between都没有时，窗口规范默认是分组下所有行（rows between unbounded preceding and unbounded following）