根据解释计划，在重写此查询时需要帮助，该查询多次使用相同的数据集

Question

我们的开发团队运行了一个查询，该查询占用大量资源，并且查看解释计划，它似乎多次使用相同的数据集。无论如何我们可以重写这个查询。

现在，我尝试将关联查询替换为直接连接，但除了一个细微差别之外，多个关联查询看起来仍然相同。

select tb2.mktg_id, mktg_cd , count(distinct tb2.conf_id) 
  from
(select conf_id, count(distinct c.mktg_id) as num_cpg 
   from acc_latst c, off_latst ot 
  where c.mktg_id = ot.mktg_id and c.bus_eff_dt > '2019-01-01' and to_date(strt_tms) = '2019-01-10'  
  group by conf_id 
 having count(distinct c.mktg_id) >1 
)tb1,
(select distinct conf_id, c.mktg_id, mktg_cd 
   from acc_latst c, off_latst ot 
  where c.mktg_id = ot.mktg_id and c.bus_eff_dt > '2019-01-01' and to_date(strt_tms) = '2019-01-10'
)tb2
  where tb1.conf_id = tb2.conf_id group by tb2.mktg_id, mktg_cd 

Answer 1

一种方法是使用 CTE -

with res1 as 
(
select distinct conf_id, c.mktg_id, mktg_cd 
   from acc_latst c, off_latst ot 
  where c.mktg_id = ot.mktg_id and c.bus_eff_dt > '2019-01-01' and to_date(strt_tms) = '2019-01-10'
)
,res2 as
(
select conf_id, count(distinct c.mktg_id) as num_cpg
from res1 group by conf_id having count(distinct c.mktg_id) > 1
)
select res1.mktg_id, mktg_cd, count(distinct res1.conf_id)  from res1 t1 inner join res2 t2 on t1.conf_id=t2.conf_id group by res1.mktg_id, mktg_cd;

如果查询仍然很慢，能否提供表和分区的详细信息。