oracle sql小结（主要讲横列转换的例子）group by以及wmsys.wm_concat()的使用

---计算九月每个电厂的数量
select f_dcname，count(f_dcname) as 九月份的数量 from W_EC_PLACESTATION_COLLECT t
where f_collectdate >= TRUNC(TO_DATE('2018-09-01','yyyy-MM-dd'),'month') AND f_collectdate < TO_DATE('2018-09-30','yyyy-MM-dd')+1
group by f_dcname

----计算九月份每个电厂对应的每个日期（左链接）
select a.f_dcname，a.f_collectdate from W_EC_PLACESTATION_COLLECT a
left join W_EC_PLACESTATION_COLLECT b on a.f_dcname = b.f_dcname and a.f_collectdate= b.f_collectdate
where a.f_collectdate >= TRUNC(TO_DATE('2018-09-01','yyyy-MM-dd'),'month') AND a.f_collectdate < TO_DATE('2018-09-30','yyyy-MM-dd')+1
and a.f_dcname like '%光伏%'
order by a.f_dcname,a.f_collectdate

----计算九月份每个日期对应的每个电厂（group by两个字段）
select f_collectdate ,f_dcname from W_EC_PLACESTATION_COLLECT t
where f_collectdate >= TRUNC(TO_DATE('2018-09-01','yyyy-MM-dd'),'month') AND f_collectdate < TO_DATE('2018-09-30','yyyy-MM-dd')+1
and f_dcname like '%光伏%'
group by f_collectdate ,f_dcname order by f_collectdate

--合并电厂的日期（行列转换）
select f_dcname ,wmsys.wm_concat(to_char(f_collectdate,'dd')) from W_EC_PLACESTATION_COLLECT t
where f_collectdate >= TRUNC(TO_DATE('2018-09-01','yyyy-MM-dd'),'month') AND f_collectdate < TO_DATE('2018-09-30','yyyy-MM-dd')+1
group by f_dcname

--合并电厂的日期（行列转换）并让合并的日期进行排序
select f_dcname ,max(r)
from (
select f_dcname , wmsys.wm_concat(to_char(f_collectdate,'dd'))
over(partition by f_dcname order by f_collectdate ) r
from W_EC_PLACESTATION_COLLECT t
where f_collectdate >= TRUNC(TO_DATE('2018-09-01','yyyy-MM-dd'),'month') AND f_collectdate < TO_DATE('2018-09-30','yyyy-MM-dd')+1
)
group by f_dcname