记得前几天看到一个帖子,说面试经常问到要怎么读取第31-40条记录数据,看到大家都争先恐后地写各种sql语句
疑惑:分不分页读取数据?读第几条到第几条的数据?跟sql语句有关吗?
- VB.NET code
CurrentIndex=4PageSize=10Dim da As OleDbDataAdapter = New OleDbDataAdapter(sql, conn)Dim ds As DataSet = New DataSet()da.Fill(ds, (CurrentIndex - 1) * PageSize, PageSize, "TmpTable")
上面是我写的分页读取数据代码,咋发现跟sql语句没有任何关系呀!
请大家说说自己都是如何分页读取数据的?
另外,我上面的代码是读取的全部的数据还是就读了10条数据?
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本质都是要转化为SQL语句
mysql里面有limit,mssql没有,一般是top颠颠倒倒法或者row_number+between。
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da.Fill(ds, (CurrentIndex - 1) * PageSize, PageSize, "TmpTable")
楼主的这个分页其实是假分页,数据表中记录数多时效率极低,因为你每次都把所有记录select出来,再由数据适配器选择出要的部分。
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分页语句和说明参考:http://www.cnblogs.com/jyk/archive/2008/08/04/1260406
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Dim da As OleDbDataAdapter = New OleDbDataAdapter(sql, conn)
这里有个参数sql. 把这个参数值贴出来 , 就知道了.
应该是读的所有数据. 不是数据库分页.
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看看这个,然后照着改:
- SQL code
declare @iPageSize int =20declare @iCurrentPage int =2declare @sSql varchar(4000)='Select Top ' + convert(varchar,@iPageSize) + ' * from tblDiary where DiaryID not in( select top ' + convert(varchar,@iPageSize * @iCurrentPage) + ' DiaryID from tblDiary order by DiaryID asc) order by DiaryID asc'--PRINT @sSqlexec(@sSql)
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- C# code
public string GetSelectSectionSql(string select, string from, string where, string orderBy, int startIndex, int sectionSize) { return String.Format("select * from (select {0}, Row_Number() over (Order by {1}) as Row_Number from {2} where {3}) TempTable where Row_Number > {4} and Row_Number <= {5}", select, orderBy, from, where, startIndex, startIndex + sectionSize); }
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用一条sql就可以了.
PageIndex,PageSize 这个是参数。
- SQL code
int Start = ((PageIndex - 1) * PageSize) + 1; int End = (PageIndex) * PageSize; string sql = "select * from (select *,ROW_NUMBER() OVER(order by " + id + ") as rownumber from table ) as tmp where rownumber between CAST(" + Start + " as varchar(10)) and CAST(" + End + " as varchar(10))