sql优化实战 把full join改为left join +union all(从5分钟降为10秒)
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2022-06-18 23:25:54
今天收到一个需求,要改写一个报表的逻辑,当改完之后,再次运行,发现运行超时。因为特殊原因,无法访问客户的服务器,没办法查看sql的执行计划、没办法知道表中的索引情况,所以,尝试从语句的改写上来优化。一...
今天收到一个需求,要改写一个报表的逻辑,当改完之后,再次运行,发现运行超时。
因为特殊原因,无法访问客户的服务器,没办法查看sql的执行计划、没办法知道表中的索引情况,所以,尝试从语句的改写上来优化。
一、原始语句如下:
select isnull(vv.customer_id,v.customer_id) as customer_id, isnull(vv.business_date,replace(v.business_date,'-','')) as business_date, v.prod_id, v.sales, vv.visit_count, v.all_sales from ( select a.customer_id , max(month)+'-01' as business_date, a.prod_id , sum(cast(value as numeric(38, 3))) sales, sum(sum(cast(value as numeric(38, 3)))) over(partition by a.customer_id) as all_sales from tb_import_sales a where a.customer_id is not null and a.prod_id is not null and a.month='2016-11' group by a.customer_id , a.prod_id )v full join ( select customer_id, max(a.business_date) as business_date, count(*) as visit_count from tb_call_store a with(nolock) inner join tb_time d on a.business_date = d.t_date where d.section ='2016-11' group by customer_id )vv on v.customer_id = vv.customer_id
原来是left join,虽然查询比较慢,但是2分钟能查出来,现在按照业务要求,需要看到所有数据,所以改成了full join,改了之后5分钟都查不出结果。
二、改写后的代码
select v.customer_id, replace(max(v.business_date),'-','') as business_date, v.prod_id, max(v.sales_volume) sales_volume , max(v.visit_count) visit_count, max(v.all_sales_volume) all_sales_volume from ( select a.customer_id , max(biz_month)+'-01' as business_date, a.prod_id , sum(cast(value1 as numeric(38, 8))) sales_volume, sum(sum(cast(value1 as numeric(38, 8)))) over(partition by a.customer_id) as all_sales_volume, null as visit_count from tb_import_sales a where a.customer_id is not null and a.prod_id is not null and a.month='2016-11' group by a.customer_id , a.prod_id union all select customer_id, max(a.business_date) as business_date, p.prod_id, null, null, count(*) as visit_count from tb_call_store a with(nolock) cross apply ( select top 1 prod_id from tb_product with(nolock) )p inner join tb_time d on a.business_date = d.t_date where d.section ='2016-11' group by customer_id,p.prod_id )v group by v.customer_id, v.prod_id
由于代码本身比较简单,没办法再进一步简化,而由于连接不了服务器,其他的方法也用不上,甚至没办法分析到底是什么导致运行这么慢。
想了想,full join 本质上就是 2次left join+union ,无非就是合并数据,于是尝试一下用union all来直接合并数据,现在改成unoin all最后,就不需要full join。
但是考虑到第2段代码中并没有prod_id这个字段,所以这里在第2段代码加上了cross apply随便取出一个产品的id,这样就有prod_id这个字段,可以合并了。
修改之后,果然速度降到了10多秒。
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