基本语法：
Func( value_expression) OVER ( [<partition_by_clause>] [<order_by_clause>] [<frame_spec_clause>] )
<partition_by_clause> = PARTITION BY <value_expression> [, ...]+
<order_by_clause> = ORDER BY <value_expression> [asc | desc] [nulls {first|last}] [, ...]+
<frame_spec_clause> = <frame_extent> [<exclusion clause>]<frame_extent> =
ROWS UNBOUNDED PRECEDING
|ROWS <constant> PRECEDING
|ROWS CURRENT ROW
|RANGE UNBOUNDED PRECEDING
|RANGE <constant> PRECEDING
|RANGE CURRENT ROW
|ROWS BETWEEN {UNBOUNDED PRECEDING| <constant> PRECEDING | CURRENT
ROW } AND { UNBOUNDED FOLLOWING | <constant> FOLLOWING | CURRENT ROW }
|RANGE BETWEEN {UNBOUNDED PRECEDING| <constant> PRECEDING | CURRENT
ROW } AND { UNBOUNDED FOLLOWING | <constant> FOLLOWING | CURRENT ROW }
<exclusion_clause> = EXCLUDE CURRENT ROW | EXCLUDE TIES | EXCLUDE
GROUP | EXCLUDE NO OTHERS
根据分析函数中的窗口特点基本可以分为两大类：
1，row_number(), lead() , lag()...
该类别over字句中必须有order by，且不能再指定窗口范围（frame_spec_clause）
2, max(), count(), sum(), first(), last()...
若将每个partition分组后的所有记录集合按order by字段排序形成队列集合S.
若没有指定order by语句，默认窗口范围为全集S
若指定order by语句，默认窗口范围为从队首[S1-SCURRENT]
若指定order by语句同时也指定窗口范围，则按窗口范围来进行计算
参考文章：
http://www.cnblogs.com/CareySon/p/3411176.html
Netezza SQL Analytic Functions 分析函数
原文：http://www.cnblogs.com/davablog/p/5074310.html