在UNION中使用Order By NULL

Question

我有一个查询(见下文),我有一个自定义开发的UDF,用于计算某些点是否在多边形(UNION中的第一个查询)或循环(UNION中的第二个查询)形状内.

select  e.inquiry_match_type_id 
        , a.geo_boundary_id 
        , GeoBoundaryContains(c.tpi_geo_boundary_coverage_type_id, 29.287437, -95.055807, a.lat, a.lon, a.geo_boundary_vertex_id ) in_out 
        , e.inquiry_id 
        , e.external_id 
        , COALESCE(f.inquiry_device_id,0) inquiry_device_id 
        , b.external_info1 
        , b.external_info2 
        , b.geo_boundary_id 
        , b.geo_boundary_type_id 
from    geo_boundary_vertex a 
        join geo_boundary b on b.geo_boundary_id = a.geo_boundary_id 
        join trackpoint_index_geo_boundary_mem c on c.geo_boundary_id = b.geo_boundary_id 
        join trackpoint_index_mem d on d.trackpoint_index_id = c.trackpoint_index_id 
        join inquiry_mem e on e.inquiry_id = b.inquiry_id left 
        outer join inquiry_device_mem f on f.inquiry_id = e.inquiry_id and f.device_id = 3201 
where   d.trackpoint_index_id = 3127  
        and b.geo_boundary_type_id = 3  
        and e.expiration_date >= now() 
group by 
        a.geo_boundary_id 
UNION 
select  e.inquiry_match_type_id      
        , b.geo_boundary_id      
        , GeoBoundaryContains( c.tpi_geo_boundary_coverage_type_id, 29.287437, -95.055807, b.centroid_lat, b.centoid_lon, b.radius ) in_out      
        , e.inquiry_id      
        , e.external_id      
        , COALESCE(f.inquiry_device_id,0) inquiry_device_id      
        , b.external_info1      
        , b.external_info2      
        , b.geo_boundary_id      
        , b.geo_boundary_type_id 
from    geo_boundary b 
        join trackpoint_index_geo_boundary_mem c on c.geo_boundary_id = b.geo_boundary_id 
        join trackpoint_index_mem d on d.trackpoint_index_id = c.trackpoint_index_id 
        join inquiry_mem e on e.inquiry_id = b.inquiry_id 
        left outer join inquiry_device_mem f on f.inquiry_id = e.inquiry_id and f.device_id = 3201 
where   d.trackpoint_index_id = 3127  
        and b.geo_boundary_type_id = 2  
        and e.expiration_date >= now() 
group by
        b.geo_boundary_id 

当我为查询运行解释时,我得到以下内容:

 id      select_type     table       type     possible_keys                                                                                                                                              key                                  key_len     ref                       rows     Extra                           
 ------  --------------  ----------  -------  ---------------------------------------------------------------------------------------------------------------------------------------------------------  -----------------------------------  ----------  ------------------------  -------  ------------------------------- 
 1       PRIMARY         d           const    PRIMARY                                                                                                                                                    PRIMARY                              4           const                     1        Using temporary; Using filesort 
 1       PRIMARY         c           ref      PRIMARY,fk_mtp_idx_geo_boundary_mtp_idx,fk_mtp_idx_geo_boundary_geo_boundary,fk_mtp_idx_geo_boundary_mtp_mem_idx,fk_mtp_idx_geo_boundary_geo_boundary_mem  fk_mtp_idx_geo_boundary_mtp_idx      4           const                     9                                        
 1       PRIMARY         b           eq_ref   PRIMARY,fk_geo_boundary_inquiry,fk_geo_boundary_geo_boundary_type                                                                                          PRIMARY                              4           gothim.c.geo_boundary_id  1        Using where                     
 1       PRIMARY         e           eq_ref   PRIMARY                                                                                                                                                    PRIMARY                              4           gothim.b.inquiry_id       1        Using where                     
 1       PRIMARY         f           ref      fk_inquiry_device_mem_inquiry                                                                                                                              fk_inquiry_device_mem_inquiry        4           gothim.e.inquiry_id       2                                        
 1       PRIMARY         a           ref      fk_geo_boundary_vertex_geo_boundary                                                                                                                        fk_geo_boundary_vertex_geo_boundary  4           gothim.b.geo_boundary_id  11       Using where                     
 2       UNION           d           const    PRIMARY                                                                                                                                                    PRIMARY                              4           const                     1        Using temporary; Using filesort 
 2       UNION           c           ref      PRIMARY,fk_mtp_idx_geo_boundary_mtp_idx,fk_mtp_idx_geo_boundary_geo_boundary,fk_mtp_idx_geo_boundary_mtp_mem_idx,fk_mtp_idx_geo_boundary_geo_boundary_mem  fk_mtp_idx_geo_boundary_mtp_idx      4           const                     9                                        
 2       UNION           b           eq_ref   PRIMARY,fk_geo_boundary_inquiry,fk_geo_boundary_geo_boundary_type                                                                                          PRIMARY                              4           gothim.c.geo_boundary_id  1        Using where                     
 2       UNION           e           eq_ref   PRIMARY                                                                                                                                                    PRIMARY                              4           gothim.b.inquiry_id       1        Using where                     
 2       UNION           f           ref      fk_inquiry_device_mem_inquiry                                                                                                                              fk_inquiry_device_mem_inquiry        4           gothim.e.inquiry_id       2                                        
 (null)  UNION RESULT    <union1,2>  ALL      (null)                                                                                                                                                     (null)                               (null)      (null)                    (null)   Using filesort                  

 12 record(s) selected [Fetch MetaData: 1ms] [Fetch Data: 5ms] 

现在,我可以拆分查询并使用ORDER BY NULL技巧来删除文件,但是当我尝试将它添加到UNION的末尾时它不起作用.

我正在考虑将查询分成2个查询或者可能完全重写它不使用UNION(当然这有点困难).我反对的另一件事就是我们已经开始使用它了,我想限制更改 - 我本来希望能够在查询结束时添加ORDER BY NULL并完成它,但是它与UNION不起作用.

任何帮助将不胜感激.

Answer 1

通常,ORDER BY可以在以下内容中用于单个查询UNION:

(
SELECT  *
FROM    table1, …
GROUP BY
        id
ORDER BY 
        NULL
)
UNION ALL
(
SELECT  *
FROM    table2, …
GROUP BY
        id
ORDER BY 
        NULL
)

但是,正如文档所述:

但是,ORDER BY对于单个SELECT语句的使用并不意味着行在最终结果中出现的顺序,因为UNION默认情况下会生成一组无序行.因此,ORDER BY在此上下文中的使用通常与结合使用LIMIT,以便它用于确定要检索的所选行的子集SELECT,即使它不一定影响最终UNION结果中那些行的顺序.如果ORDER BY没有出现LIMIT在SELECT,它被优化掉,因为它不会有任何效果呢.

然而,这当然是一个聪明的举动,并不太聪明,因为他们也忘了优化排序行为GROUP BY.

至于现在,您应该LIMIT为您的个人查询添加一个非常高的:

(
SELECT  *
FROM    table1, …
GROUP BY
        id
ORDER BY 
        NULL
LIMIT 100000000
)
UNION ALL
(
SELECT  *
FROM    table2, …
GROUP BY
        id
ORDER BY 
        NULL
LIMIT 100000000
)

我将它作为一个错误发布到MySQL,希望他们能在下一个版本中修复它,但同时你可以使用这个解决方案.

请注意,类似的解决方案(使用TOP 100%)用于强制子查询的排序SQL Server 2000,但是,它停止工作2005(对于优化器的ORDER BY子查询没有影响TOP 100%).

使用它是安全的,因为即使优化器行为在下一个版本中发生变化,它也不会破坏您的查询,但只会使它们像现在一样慢.