Question

这里我有一个查询场景，解释了内联注释的范围：

select 
    -- selecting both entity ids
    entity_a.id as entity_a_id, 
    entity_b.id as entity_b_id,
    concat(entity_a.id, entity_b.id) as `key`

from `entity_b` 

-- Following are few one to many relations to match entity a with b
inner join `entity_b_function` on 
    `entity_b`.`id` = `entity_b_function`.`entity_b_id` 
inner join `entity_b_category` on 
    `entity_b`.`id` = `entity_b_category`.`entity_b_id` 
inner join `entity_b_scope` on 
    `entity_b`.`id` = `entity_b_scope`.`entity_b_id` 

inner join `entity_a` on 
    `entity_a`.`category_id` = `entity_b_category`.`category_id` and 
    `entity_a`.`scope_id` = `entity_b_scope`.`scope_id` 
inner join `entity_a_function` on 
    `entity_b_function`.`function_id` = `entity_a_function`.`function_id` 


-- pivot of entity a and b
-- making sure matching entities are finally related in pivot
left join `entity_a_b_pivot` on 
    `entity_a_b_pivot`.`entity_a_id` = `entity_a`.`id` and 
    `entity_a_b_pivot`.`entity_b_id` = `entity_b`.`id` 

where 
    -- we need only matching entities which are not yet related in pivot
    `entity_a_b_pivot`.`id` is null and 
    -- when both entities are active in the system
    `entity_b`.`status` = 1 and 
    `entity_a`.`status` = 1 
LIMIT 5000;

目前的结果如下：
（由于一对多关系的连接，指出的项目是重复的）

entity_a_id,    entity_b_id     key
    1               1           11
>   1               1           11
    1               2           12
    2               1           21
    2               2           22
>   2               2           22

在这里，如果我使用GROUP BY key或DISTINCT(key)来消除重复项，那么查询处理将永远停留在100％的CPU使用率上但没有这些只是眨眼就能返回5K记录但是只有90 ％重复。

如何针对不同结果优化查询？

Answer 1

如何在选择列表的开头添加DISTINCT呢？

select 
    -- selecting both entity ids
    distinct
    entity_a.id as entity_a_id, 
    entity_b.id as entity_b_id,
    concat(entity_a.id, entity_b.id) as `key`

from `entity_b` 

-- Following are few one to many relations to match entity a with b
inner join `entity_b_function` on 
    `entity_b`.`id` = `entity_b_function`.`entity_b_id` 
inner join `entity_b_category` on 
    `entity_b`.`id` = `entity_b_category`.`entity_b_id` 
inner join `entity_b_scope` on 
    `entity_b`.`id` = `entity_b_scope`.`entity_b_id` 

inner join `entity_a` on 
    `entity_a`.`category_id` = `entity_b_category`.`category_id` and 
    `entity_a`.`scope_id` = `entity_b_scope`.`scope_id` 
inner join `entity_a_function` on 
    `entity_b_function`.`function_id` = `entity_a_function`.`function_id` 


-- pivot of entity a and b
-- making sure matching entities are finally related in pivot
left join `entity_a_b_pivot` on 
    `entity_a_b_pivot`.`entity_a_id` = `entity_a`.`id` and 
    `entity_a_b_pivot`.`entity_b_id` = `entity_b`.`id` 

where 
    -- we need only matching entities which are not yet related in pivot
    `entity_a_b_pivot`.`id` is null and 
    -- when both entities are active in the system
    `entity_b`.`status` = 1 and 
    `entity_a`.`status` = 1 
LIMIT 5000;

使用group by或distinct删除重复

1 个答案: