是否可以为下面的SQL查询删除UNION

Question

我想优化下面的查询。一小部分记录需要2分钟以上的时间。是否可以删除UNION并优化查询

Select cia.cia_orderamount, cia.cia_notes, cia.cia_mincount, cia.cia_customerid, cia.cia_id, cia.cia_locationid, lc.locationcode, T1.instock, c.id as customerid, c.customer
From cardinventoryalerts cia
Inner join customers c on cia.cia_customerid = c.id and c.useautocardorder = 1
Inner Join locationcodes lc on cia.cia_locationid = lc.id
left JOIN 
  (SELECT cb.customer, Case when cb.locationcode is null or cb.locationcode = '' Then NULL Else cb.locationcode End as locationcode,
    sum( CASE WHEN cb.issued = 'no' THEN 1 ELSE 0 END) as instock
  FROM cardbatch cb
  Group By cb.customer, cb.locationcode
  ) as T1 on lc.locationcode = T1.locationcode and T1.customer = c.customer
WHERE (cia_mincount > T1.instock or T1.instock is NULL)

UNION
Select cia.cia_orderamount, cia.cia_notes, cia.cia_mincount, cia.cia_customerid, cia.cia_id, -1, NULL, T1.instock, c.id as customerid, c.customer
From cardinventoryalerts cia
Inner join customers c on cia.cia_customerid = c.id and c.useautocardorder = 1
left JOIN 
  (SELECT cb.customer, -1, sum( CASE WHEN cb.issued = 'no' THEN 1 ELSE 0 END) as instock
  FROM cardbatch cb
  where cb.locationcode is null or cb.locationcode = ''
  Group By cb.customer
  ) as T1 on c.customer = T1.customer
WHERE (cia_mincount > T1.instock or T1.instock is NULL) and cia.cia_locationid is null

对此查询的解释：

    UNION RESULT    <union1,3>  ALL                     
1   PRIMARY c   ALL PRIMARY,id              2   Using where
1   PRIMARY cia ALL fk_ciacustid,fk_cialocationid               3   Using where
1   PRIMARY lc  eq_ref  PRIMARY,id  PRIMARY ... quiz.cia.cia_locationid 1   
1   PRIMARY <derived2>  ALL                 3   Using where
2   DERIVED cb  index       customer_loc    ...     3   
3   UNION   cia ref fk_ciacustid,fk_cialocationid   fk_cialocationid    ... const   1   Using where
3   UNION   c   eq_ref  PRIMARY,id  PRIMARY ... quiz.cia.cia_customerid 1   Using where
3   UNION   <derived4>  ALL                 1   Using where
4   DERIVED cb  index       customer_loc    ...     3   Using where

Answer 1

我认为您可以将这两个部分结合在一起(参见下面)，将内部连接位置代码替换为左联接位置代码，并在条件适当的情况下编写

From cardinventoryalerts cia
Inner join customers c on cia.cia_customerid = c.id and c.useautocardorder = 1
left Join locationcodes lc on cia.cia_locationid = lc.id
left JOIN 
  (SELECT cb.customer, Case when cb.locationcode is null or cb.locationcode = '' Then NULL Else cb.locationcode End as locationcode,
    sum( CASE WHEN cb.issued = 'no' THEN 1 ELSE 0 END) as instock
  FROM cardbatch cb
  Group By cb.customer, cb.locationcode
  ) as T1 on lc.locationcode = T1.locationcode and T1.customer = c.customer
left JOIN 
  (SELECT cb.customer, -1, sum( CASE WHEN cb.issued = 'no' THEN 1 ELSE 0 END) as instock
  FROM cardbatch cb
  where cb.locationcode is null or cb.locationcode = ''
  Group By cb.customer
  ) as T1 on c.customer = T1.customer