SQL提取峰值或TOP N方法（sql提取字段前几位数字）

首先从查询得到一个数据表为A表，按max(pmRrcConnMax) 从大至小排序并给标记，如1、2、3...

然后，从A表中提取峰值或TOP N。

```

select date_id,hour_id,erbs,eutrancelltdd,

max(pmRrcConnMax_) AS pmRrcConnMax,

MAX(RANK) AS TOPN

FROM(

select date_id,hour_id,erbs,eutrancelltdd,

max(pmRrcConnMax) as pmRrcConnMax,

Row_Number() OVER (partition by eutrancelltdd ORDER BY max(pmRrcConnMax) desc) rank

from

DC_E_ERBS_EUTRANCELLTDD_RAW

where DATE_ID BETWEEN '20200327' AND '20200327'

//AND erbs IN ('')

group by date_id,hour_id,erbs,eutrancelltdd

)A

group by date_id,hour_id,erbs,eutrancelltdd

HAVING TOPN=1 OR TOPN=2 OR TOP=3

```

结果：