聚合函数（如sum()、max()等）可以计算基于组的某种聚合值，但是聚合函数对于某个组只能返回一行记录。若想对于某组返回多行记录，则需要使用分析函数over()。
语法
分析函数带有一个开窗函数over()，包含三个分析子句:
分组(partition by) 排序(order by) 窗口(rows)
窗口函数语法：
第一行至当前行：
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW当前行至最后一行：
ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING当前行的上一行(rownum-1)到当前行：
ROWS BETWEEN 1 PRECEDING AND CURRENT ROW当前行的上一行(rownum-1)到当前行的下辆行(rownum+2)：
ROWS BETWEEN 1 PRECEDING AND 2 FOLLOWING示例
根据用户查询每个应用的消息数和每个应用的第一条消息的文本
select * from (select T_HTHZ_XX_YDMX.*, T_HTHZ_XX_FSDL.clsj, temp1.*,T_HTHZ_XX_FSDL.xxwb, (select count(*) from T_HTHZ_XX_YDMX t
where t.tzdx = ? and t.ydsj is null and t.ywxt = t_hthz_xx_ydmx.ywxt) num,ROW_NUMBER() over(partition by T_HTHZ_XX_YDMX.ywxt
order by T_HTHZ_XX_FSDL.clsj desc) rn from T_HTHZ_XX_YDMX left join T_HTHZ_XX_FSDL on T_HTHZ_XX_FSDL.dlbm = T_HTHZ_XX_YDMX.dlbmleft
join (select yymc, yyid, STORE_NAME from T_HTHZ_MH_FWDTYY, T_HTHZ_SYS_FILE_INDEX where T_HTHZ_MH_FWDTYY.YYTB =
T_HTHZ_SYS_FILE_INDEX.STORE_TOKEN and T_HTHZ_MH_FWDTYY.YYZT='Y' and T_HTHZ_MH_FWDTYY.QYSJ <= sysdate and (T_HTHZ_MH_FWDTYY.TYSJ is
null or T_HTHZ_MH_FWDTYY.TYSJ >= sysdate) ) temp1 on temp1.yyid = T_HTHZ_XX_YDMX.ywxtwhere T_HTHZ_XX_YDMX.tzdx = ?) temp2 where
rn = 1 order by clsj desc