请教一个sql语句

表1：
1 2010-01 120
2 2010-02 200
3 2010-03 400

如果写一个sql，得到累计数，如下：
1 2010-01 120
2 2010-02 320
3 2010-03 720

多谢！！！

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nobody knows？

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select id,month,sum(num) over (order by id,month) num from table;

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引用

select id,month,sum(num) over (order by id,month) num from table;

学习

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如果还有分类，怎么累计？多谢回复
1 2010-01 120 a
2 2010-02 200 a
3 2010-03 400 b

1 2010-01 120 a
2 2010-02 320 a
3 2010-03 400 b

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select id,month,sum(num) over (partition by type order by id,month) num,type from table;

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SQL code:
with temp as(
select 1 id,to_date('2010-01','yyyy-mm') date1,120 num from dual
union all
select 2 id,to_date('2010-02','yyyy-mm') date1,200 num from dual
union all
select 3 id,to_date('2010-03','yyyy-mm') date1,400 num from dual
union all
select 4 id,to_date('2010-03','yyyy-mm') date1,400 num from dual
)
select date1,sum(num) over(partition by date1 order by id,date1) total from temp