初学者如何学习分析函数

经常发现一些网友问分析函数的问题，虽然分析函数比较多，有一些分析函数也确实比较难以理解，会给初学者有很大的心理压力，其实对于大部分的分析函数，一般都不会有机会用到，所以掌握常用的几个分析函数就可以啦。

常用的分析函数如下所列:
row_number() over(partition by ... order by ...)
rank() over(partition by ... order by ...)
dense_rank() over(partition by ... order by ...)
count() over(partition by ... order by ...)
max() over(partition by ... order by ...)
min() over(partition by ... order by ...)
sum() over(partition by ... order by ...)
avg() over(partition by ... order by ...)
first_value() over(partition by ... order by ...)
last_value() over(partition by ... order by ...)
lag() over(partition by ... order by ...)
lead() over(partition by ... order by ...)

示例：
14:33:29 SQL> select type,qty from test;
TYPE QTY
---------- ----------
1 3
1 6
2 5
2 9
2 7

14:33:36 SQL> select type,qty,to_char(row_number() over(partition by type order by qty))||"/"||to_char(count(*) over(partition by type)) as cnt2 from test;
TYPE QTY CNT2
---------- ---------- ------------
1 3 1/2
1 6 2/2
2 5 1/3
2 7 2/3
2 9 3/3