MySQL查询案例陈述在哪里进行优化

Question

我在mysql中写一个查询，我对递归查询并不熟悉。 由于我提出的条件看起来不太好，因此我应该如何以及如何对以下查询进行优化，因此必须有一种更简单的方法。

 select
   b.entity_id 
from
   entity_hierarchies a,
   entity_hierarchies b 
where
   a.entity_id = 25 
   and a.entity_type = 'user' 
   and b.entity_type = 'idea' 
   and a.Geography_Geography = 
   case
      when
         a.Geography_Geography is null 
      then
         a.Geography_Geography 
      else
         b.Geography_Geography 
   end
   and COALESCE(a.Geography_Country, '') = 
   case
      when
         a.Geography_Country is null 
      then
         COALESCE(a.Geography_Country, '') 
      else
         b.Geography_Country 
   end
   and COALESCE(a.Geography_DistrictOrCounty, '') = 
   case
      when
         a.Geography_DistrictOrCounty is null 
      then
         COALESCE(a.Geography_DistrictOrCounty, '') 
      else
         b.Geography_DistrictOrCounty 
   end
   and COALESCE(a.Geography_State, '') = 
   case
      when
         a.Geography_State is null 
      then
         COALESCE(a.Geography_State, '') 
      else
         b.Geography_State 
   end
   and COALESCE(a.Geography_City, '') = 
   case
      when
         a.Geography_City is null 
      then
         COALESCE(a.Geography_City, '') 
      else
         b.Geography_City 
   end

Answer 1

简介

我注意到您可以用更简单的形式重写其中一些语句。

例如：

and a.Geography_Geography = 
   case
      when
         a.Geography_Geography is null 
      then
         a.Geography_Geography 
      else
         b.Geography_Geography 
   end

可以简单地变成：

AND ( a.Geography_Geography is null or a.Geography_Geography =   b.Geography_Geography )

最终解决方案

select
   b.entity_id 
from
   entity_hierarchies a,
   entity_hierarchies b 
where
   a.entity_id = 25 
   and a.entity_type = 'user' 
   and b.entity_type = 'idea' 
AND ( a.Geography_Geography is null OR a.Geography_Geography =   b.Geography_Geography )
AND ( a.Geography_Country is null  OR  a.Geography_Geography = b.Geography_Country )
AND ( a.Geography_DistrictOrCounty is null  OR a.Geography_DistrictOrCounty =  b.Geography_DistrictOrCounty )
AND (   a.Geography_State is null  OR   a.Geography_State =   b.Geography_State )
AND ( a.Geography_City is null  OR  a.Geography_City =   b.Geography_City );