分析函数

1.语法

function1(argument1,argument......argumentN)  --（function处理的数据源（table)中，包含所有表的字段，不受partition-by的影响，与group by 不同）

over([partition-by-clause] [order-by-clause] [windowing-clause])

2.语法解释

argument --处理的字段

partition-by --分区子句，限制function处理的上下边界

order by -- 对分区中的数据进行排序 ，当windowing-clause 为 rows between unbounded preceding and current now（当前列），影响最大

windowing-clause --是在partition-by的条件下进行限制，例如rows between unbounded preceding and unbounded following，指的是partition-by的条件下全部数据，不能跨分区

3.例子

3.1 求product, country, region,year分区下每年的销售额

select  year, week,sale,
    sum (sale) over(
          partition by product, country, region,year
          order by week  --行排序没有作用
   rows between unbounded preceding and unbounded following  --跨整个分区
           ) running_sum_ytd
  from sales_fact
  where country in ('Australia')  and product ='Xtend Memory'
  order by product, country,year, week

3.2 求product, country, region,year分区下到当前周的销售额

select  year, week,sale,
    sum (sale) over(
          partition by product, country, region,year
          order by week  --行排序起到关键性作用
   rows between unbounded preceding and current now  --没有跨整个分区，在分区首列到当前列
           ) running_sum_ytd
  from sales_fact
  where country in ('Australia')  and product ='Xtend Memory'
  order by product, country,year, week