删除一个表中的重复数据同时保留第一次插入那一条以及sql优化

删除一个表中的重复数据同时保留第一次插入那一条以及sql优化

 

       业务：一个表中有很多数据（id为自增主键），在这些数据中有个别数据出现了重复的数据。

 

       目标：需要把这些重复数据删除同时保留第一次插入的那一条数据，还要保持其它的数据不受影响。

 

       解题过程：

 

       第一步：查出所有要保留的下来的数据的id（save_id）
[sql] 
select id as save_id  
  from yujing.alarm_event_info_snapshot aeis  
 where aeis.event_id in  
       (select ae.id  
          from yujing.alarm_event ae  
         where ae.event_uuid like 'yuanwtj_%')  
 group by (aeis.event_id)  
优化后：
[sql] 
select aeis.id as save_id  
  from yujing.alarm_event ae  
 right join yujing.alarm_event_info_snapshot aeis  
    on aeis.event_id = ae.id  
 where ae.event_uuid like 'yuanwtj_%'  
 group by (aeis.event_id)  
  
       第二步：获取所有相关数据的id（all_id）
[sql] 
select aeis.id as all_id  
  from yujing.alarm_event_info_snapshot aeis  
 where aeis.event_id in  
       (select ae.id  
          from yujing.alarm_event ae  
         where ae.event_uuid like 'yuanwtj_%')  
 order by aeis.event_id  
优化后：       
[sql] 
select aeis.id as all_id  
  from yujing.alarm_event ae  
 right join yujing.alarm_event_info_snapshot aeis  
    on aeis.event_id = ae.id  
 where ae.event_uuid like 'yuanwtj_%'  

        第三步：获取要删除的数据的id（del_id）
[sql] 
select ad.all_id as del_id  
  from (select aeis.id as all_id  
          from yujing.alarm_event_info_snapshot aeis  
         where aeis.event_id in  
               (select ae.id  
                  from yujing.alarm_event ae  
                 where ae.event_uuid like 'yuanwtj_%')) as ad  
 where ad.all_id not in (select id as save_id  
                           from yujing.alarm_event_info_snapshot aeis  
                          where aeis.event_id in  
                                (select ae.id  
                                   from yujing.alarm_event ae  
                                  where ae.event_uuid like 'yuanwtj_%')  
                          group by (aeis.event_id))  
优化后：
[sql] 
select ad.all_id as del_id  
  from (select aeis.id as all_id  
          from yujing.alarm_event ae  
         right join yujing.alarm_event_info_snapshot aeis  
            on aeis.event_id = ae.id  
         where ae.event_uuid like 'yuanwtj_%') as ad  
  left join (select aeis.id as save_id  
               from yujing.alarm_event ae  
              right join yujing.alarm_event_info_snapshot aeis  
                 on aeis.event_id = ae.id  
              where ae.event_uuid like 'yuanwtj_%'  
              group by (aeis.event_id)) as sd  
    on ad.all_id = sd.save_id  
 where sd.save_id is null  

 

       

       第四步：根据id删除所有节点，注意mysql中如果有大量数据时需要批量删除，我最后使用了etl工具进行的批量删除

 

       总结：在mysql中，sql语句中最好不要在in或not in关键字的查询里动态获取匹配的值，数据量大的情况下使用它们效率很低，可以使用左右连接来代替in操作，这样效率会提高很多倍，大数据量下尤为明显。