sql优化实战 把full join改为left join +union all(从5分钟降为10秒)

sql优化实战 把full join改为left join +union all(从5分钟降为10秒)

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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原文链接:https://blog.csdn.net/sqlserverdiscovery/article/details/53542543