sql優化實戰:把full join改為left join +union all(從5分鐘降為10秒)
阿新 • • 發佈:2018-12-23
今天收到一個需求,要改寫一個報表的邏輯,當改完之後,再次執行,發現執行超時。
因為特殊原因,無法訪問客戶的伺服器,沒辦法檢視sql的執行計劃、沒辦法知道表中的索引情況,所以,嘗試從語句的改寫上來優化。
一、原始語句如下:
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
原來是left join,雖然查詢比較慢,但是2分鐘能查出來,現在按照業務要求,需要看到所有資料,所以改成了full join,改了之後5分鐘都查不出結果。
二、改寫後的程式碼
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
由於程式碼本身比較簡單,沒辦法再進一步簡化,而由於連線不了伺服器,其他的方法也用不上,甚至沒辦法分析到底是什麼導致執行這麼慢。
想了想,full join 本質上就是 2次left join+union ,無非就是合併資料,於是嘗試一下用union all來直接合並資料,現在改成unoin all最後,就不需要full join。
但是考慮到第2段程式碼中並沒有prod_id這個欄位,所以這裡在第2段程式碼加上了cross apply隨便取出一個產品的id,這樣就有prod_id這個欄位,可以合併了。
修改之後,果然速度降到了10多秒。