SQL删除重复的条目的最简单方法
SQL删除重复的条目的最简单方法,其实没有,删除重复的条目嘛,其实用这个修改一下完全可以的哦,只是提供一个思路,就是把要检查
评教系统最后的一项工作,就是对数据进行整理,这个万恶之源就是允许了学生自己选课,,当然这个功能的开放,也使得老师减少了一点工作量。对于此功能的评价不再多说。下面开始进入话题:
评教系统要删除的不是重复的条目,而是项目比较少的条目。先说下原因:课程的授予,一般是有教学秘书进行授课的,但是漏授的事情频繁发生,这就造成了有的学生上的课,评价界面却没有,负责的学生就自己选了,但是很有可能选错或者只有极个别人选,那么对于此老师教的此课,只有少数人评价,那么这就属于无效数据,是我们要删除的。
下面说下我的思路的一步步转变:
第一印象是从后台界面找到那条记录,查询老师、课程分别对应的ID,再在评价结果表里面进行更改,我没有这样做,也没有去尝试。
我们是学编程的,对于重复的事情,一定不可以自己去做,所以我就努力的想sql语句进行删除。期间进行了各种嵌套,我的思路是首先把评教人次少于10(一般多于10的我们就认为其有一定效应),然后从这个查询出来的结果中提取出来教师ID以及课程ID,然后通过一个delete语句进行删除,
悲剧的是我弄了一整天也没弄出来,我先附一下没有弄出来的代码,希望高手指出怎么才可以修改正确。
TheoryResult是评价结果表,201201是一个时间限定,说明是2012年上半年,其他的with rollup被注释掉了,这里用不上。我的这个代码完全是按照上面的思路进行的,但是没有成功。
后来果断选择更简单的方法,那就是通过程序将其进行关联。代码是最美的,也是最能说明白问题的,下面看代码:
用了一个while循环,这个效率的问题嘛,是低一点点,但是比你手动删除要快很多,个人感觉还是sql语句执行的要快点,所以写成存储过程可能会好一点点。
看到这里你是不是感觉有种上当的感觉呢?其实没有,删除重复的条目嘛,其实用这个修改一下完全可以的哦,只是提供一个思路,就是把要检查的重复列在group by中体现,在while循环中套一个for循环,for循环对tcount进行遍历,如果有3个,你删除2个那样不可以了嘛。

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