SQL中遇到多条相同内容只取一条的最简单实现

　　从多个版本记录中保留最新版本

* 二层分支的情况:
* SELECT obj FROM ZxlPrdRequestModule obj
* LEFT JOIN ZxlPrdProductBranchFilter ppbf ON ppbf.hid=obj.hid
* AND ppbf.branchProductId IN :productIdList
* WHERE ( (obj.zxlPrdId=:zxlPrdId AND obj.active=1)
* OR (obj.zxlPrdId=:baseProductId1 AND obj.versionId<=:baseProductVersionId1 AND ppbf.active IS NULL)
* OR (obj.zxlPrdId=:baseProductId2 AND obj.versionId<=:baseProductVersionId2 AND ppbf.active IS NULL) )
* AND NOT (obj.editOpType='DELETE' AND obj.editOpStatus='CONFIRMED')
*
* AND NOT EXISTS(SELECT 1 FROM ZxlPrdRequestModule _obj
* WHERE ( (_obj.zxlPrdId=:zxlPrdId AND _obj.active=1)
* OR (_obj.zxlPrdId=:baseProductId1 AND _obj.versionId<=:baseProductVersionId1 AND ppbf.active IS NULL)
* OR (_obj.zxlPrdId=:baseProductId2 AND _obj.versionId<=:baseProductVersionId2 AND ppbf.active IS NULL) )
* AND NOT (_obj.editOpType='DELETE' AND _obj.editOpStatus='CONFIRMED')
* AND obj.moduleId=_obj.moduleId AND obj.versionId<_obj.versionId)

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转自：SQL中遇到多条相同内容只取一条的最简单实现

SQL中经常遇到如下情况，在一张表中有两条记录基本完全一样，某个或某几个字段有些许差别， 这时候可能需要我们踢出这些有差别的数据，即两条或多条记录中只保留一项。 

如下：表timeand

针对time字段相同时有不同total和name的情形，每当遇到相同的则只取其中一条数据，最简单的实现方法有两种

每当遇到相同的则只取其中一条数据，最简单的实现方法有两种

 

1、select time,max(total) as total,name from timeand group by time;//取记录中total最大的值

 

或 select time,min(total) as total,name from timeand group by time;//取记录中total最小的值

 

上述两种方案都有个缺点，就是无法区分name字段的内容，所以一般用于只有两条字段或其他字段内容完全一致的情况

 

2、select * from timeand as a where not exists(select 1 from timeand where a.time = time and a.total<total);

 

此中方案排除了方案1中name字段不准确的问题，取的是total最大的值

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