1.    多表聚合查詢優化

在實際的業務場景中經常會需要多表關聯，需要使用到多個表的欄位關聯聚合結果，對於新手來說，最直觀的想法就是把所有資料來源join成一張大表，再在大表中進行指標的計算，但是這樣子就會效率非常低下

最好的方法就是：

先把多張表的資料進行欄位聚合，再在聚合過後的基礎上進行表關聯

例如：

表A： adv_id, date, ad_id, material_id,ad_name, self_imp, self_click

表B：adv_id, date,ad_id,material_id,ad_name,target_imp_taget_click

表C； adv_id, date,ad_id,material_id,ad_name,third_imp,third_click

需要的查詢結果；adv_id，self_imp, self_click, target_imp_taget_click, third_imp,third_click

最好的查詢方案：

select t1.*, t2.targt_imp,t2.target_click,t3.third_imp,t3.third_click

from

(select adv_id,, sum(self_imp)as self_imp,sum(self_click) as self_click from table_A  group by adv_id) t1

left join

(select adv_id, sum(target_imp) astarget_imp, sum(target_click) as target_click from table B group by adv_id) t2

on t1.adv_id=t2.adv_id

left join

(select adv_id, sum(third_imp) as third_imp,sum(third_click) as third_click from table C group by adv_id) t3

on t1.adv_id=t3.adv_id