blocks|key|1292900|text|乔治,|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1292901|答案是否定的。|1292902|实际上，可以在内部使用某种类型的索引，但仅作为实现细节。例如，如果您创建了一个外键约束，那么它可能会得到索引的帮助。但这对开发人员来说无关紧要。|1292903|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

George,

The answer is no.

Actually, some sort of indexing may be used internally, but only as an implementation detail. For instance, if you create a foreign key constraint, maybe that's assisted by an index. But it doesn't matter to a developer.

blocks|key|1293013|text|上面的约翰是正确的。DataTables在内存结构中是断开的。它们不映射到数据库的物理实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1293014|磁盘上的索引用于加快查找速度，因为您并不需要所有的行。如果你必须加载每一行并扫描它们，这是很慢的，所以索引是有意义的。在DataTable中，您已经拥有了所有行，所以比较已经很快了。|1293015|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

John above is correct. DataTables are disconnected in memory structures. They do not map to the physical implementation of the database. 

The indexes on disk are used to speed up lookups because you don't have all the rows. If you have to load every row and scan them it is slow, so an index makes sense. In a DataTable you already have all the rows, so a comparison is fast already.

blocks|key|1293094|text|其他人则指出，DataSet不打算用作数据库系统--只是数据的表示。如果您认为DataSet就是一个数据库，那么您就错了，可能需要重新考虑您的实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1293095|如果您需要客户端数据库，请考虑使用SQL+Compact或SQL+Lite，两者都是免费的可再分发数据库系统，无需单独安装或服务即可使用。如果您需要功能更全的工具，SQL+Express将是您的下一步选择。|1293096|不过，为了帮助澄清，在.NET开发中使用数据集/表来根据需要临时保存数据。可以将它们看作是对数据库的SELECT查询的结果；它们大致类似于CSV文件或其他形式的表格数据--您可以从数据库中提取数据，处理这些数据，然后将更改推回到数据库中--但它们本身并不是数据库。|1293097|如果你有一个很大的项目集合，出于某种原因你需要保存在内存中，那么你可以考虑构建一个轻量级的DTO+(数据传输对象，Google+it，它们非常简单)并将它们加载到一个HashTable中。HashTables不会为您提供任何形式的关系数据，但在查找方面非常高效。|1293098|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Others have made the point that a DataSet is not intended to serve as a database system--just a representation of data. If you are working under the impression that a DataSet is a database then you are mistaken and might need to reconsider your implementation.

If you need a client-side database, consider using SQL Compact or SQL Lite, both are free redistributable Database systems which can be used without requiring separate installations or services. If you need something more full-featured the SQL Express is the next step up.

To help clarify though, DataSets/Tables are used in .NET development to temporarily hold data as needed. Think of them as the results of a SELECT query against a database; they are roughly similar to CSV files or other forms of tabular data--you can pull data into them from a database, work with the data, and then push the changes back to a database--but they, on their own, are not databases.

If you have a large collection of items which you need to keep in memory for one reason or another then you might consider building a lightweight DTO (data transfer object, Google it, they're very simple) and loading them into a HashTable. HashTables won't give you any form of relational data, but are very efficient at look-ups.

blocks|key|1507707|text|DataTables有一个可以用作索引的PrimaryKey字段(不管怎样，它们已经很快了)。此字段不是从数据库的主键复制的(尽管这可能很好)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1507708|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

DataTables have a PrimaryKey field that can serve as an index (they are fast already anyway). This field is not copied from the Primary Keys of the database (although that might be nice).

blocks|key|1293209|text|您可以为datatable创建主键。如果你在主键字段中搜索，过滤操作会得到很大的提升。请查看此链接：here|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1293210|entityMap|0|LINK|mutability|MUTABLE|url|http://codingcramp.blogspot.in/2009/02/datatable-performance.html^0|1E|4|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

You can create a primary key for the datatable. Filter operations get a big boost if you are searching in the primary key field. Check out this link: <a href="http://codingcramp.blogspot.in/2009/02/datatable-performance.html">here</a>

blocks|key|1507842|text|对于来自大型数据表的许多不符合主键的查询，我也遇到了同样的问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1507843|我找到的解决方案是为我想要使用的每个索引创建DataView，然后使用它的Find和FindRows方法来提取数据。|1507844|DataView在DataTable上创建一个内部索引，并为此目的虚拟地充当一个索引。|1507845|在我的例子中，我能够将10,000次查询从40秒减少到1秒！|1507846|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

I had the same problem with many queries from a large datatable that are not according to the primary key.

The solution I found was to create DataView for each index I wanted to use, and then use it's Find and FindRows methods to extract the data.

DataView creates an internal index on the DataTable and behaves virtually as an index for this purpose.

In my case I was able to reduce 10,000 queries from 40 Seconds to ONE!!!

blocks|key|1507886|text|我对文档的理解是，(如果需要)实现这一点的正确方法是使用AsDataView生成绑定到底层表的DataView+(或LinqDataView)。如果您的DataTable是不变的，那么DataView可以是静态的，以避免冗余的重新索引。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1507887|我目前正在研究Linq+to+DataSet，这个问题对我很有帮助，所以谢谢。|1507888|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.msdn.com/b/erickt/archive/2007/10/05/linq-to-dataset-data-binding-introducing-linqdataview.aspx^0|1B|8|1M|C|24|9|2K|8|S|A|0|0|7|F|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

My reading of the docs is that the correct way to achieve this (if needed) is to use <a href="http://blogs.msdn.com/b/erickt/archive/2007/10/05/linq-to-dataset-data-binding-introducing-linqdataview.aspx" rel="nofollow">AsDataView</a> to produce a <code>DataView</code> (or <code>LinqDataView</code>) that's bound to the underlying table. If your <code>DataTable</code> is invariant then the <code>DataView</code> can be static to avoid redundant re-indexing. 

I am currently investigating <code>Linq to DataSet</code>, and this q was helpful to me, so thanks.

blocks|key|1507917|text|如果您(编码器)指定一个或多个DataTables作为主键，则会对DataColumns进行索引。在内部，ADO.NET使用红黑树来形成这个索引，提供日志时间查找。此主键不会根据来自数据提供程序的任何基础键自动设置。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1507918|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

DataTables are indexed if you (the coder) specify one or more DataColumns as the Primary Key. Interally ADO.NET uses a Red-Black tree to form this index giving log-time lookups. This Primary Key is not set automatically based on any underlying keying from the data provider.

blocks|key|1293383|text|不是，但可能是。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1293384|您可以使用DataView在DataTable上设置自己的索引。当您更改表时，将重新构建DataView，因此索引应该始终是最新的。|1293385|我为我自己的应用程序做了一些工作台测试。我使用DataTable来近似Boost+MultiIndexContainer。要在名为"Author“的列上创建索引，我初始化DataTable，然后初始化DataView...|1293386|_dvChangesByAuthor+=+
++++new+DataView(
++++++++_dtChanges,+
++++++++string.Empty,+
++++++++"Author+ASC",+
++++++++DataViewRowState.CurrentRows);|code-block|syntax|javascript|1293387|然后，要从表中按作者拉取数据，可以使用视图的FindRows函数...|1293388|++++++++++++dataRowViews+=+_dvChangesByAuthor.FindRows(author);
++++++++++++List<DataRow>+returnRows+=+new+List<DataRow>();
++++++++++++foreach+(DataRowView+drv+in+dataRowViews)
++++++++++++{
++++++++++++++++returnRows.Add(drv.Row);
++++++++++++}|1293389|我随机创建了一个大的DataTable，并使用DataTable.Select()、Linq-+to+-DataSet+(通过导出到list来强制执行)和上面的DataView方法运行查询。DataView方法轻松取胜。Linq有5,000个滴答，Select有超过26000个滴答，DataView有192个滴答……|1293390|LOC=20141121-14:46:32.863,UTC=20141121-14:46:32.863,DELTA=72718,THR=9,DEBUG,LOG=Program,volumeTest()+-+Running+queries+for+author+>TFYN_AUTHOR_047<
LOC=20141121-14:46:32.863,UTC=20141121-14:46:32.863,DELTA=72718,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingLinqToDataset()+-+Query+elapsed+time:+2+ms,+4934+ticks;+Rows=65+
LOC=20141121-14:46:32.879,UTC=20141121-14:46:32.879,DELTA=72733,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingSelect()+-+Query+elapsed+time:+11+ms,+26575+ticks;+Rows=65+
LOC=20141121-14:46:32.879,UTC=20141121-14:46:32.879,DELTA=72733,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingDataview()+-+Query+elapsed+time:+0+ms,+192+ticks;+Rows=65|1293391|所以，如果你想在一个DataTable上建立索引，我建议你使用DataView，如果你能处理这样一个事实:当数据改变时，索引会被重新构建。|1293392|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|H|7|11|8|@]|9|@]|A|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|H|7|13|8|@]|9|@]|A|$I|J]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

No, but possibly yes.

You can set up your own indices on a DataTable, using a DataView. As you change the table, the DataView will be rebuilt, so the index should always be up to date.

I did some bench tests for my own app. I use a DataTable to approximate a Boost MultiIndexContainer. To create an index on a column call "Author", I initialise the DataTable, and then the DataView...

<pre><code>_dvChangesByAuthor = 
 new DataView(
 _dtChanges, 
 string.Empty, 
 "Author ASC", 
 DataViewRowState.CurrentRows);
</code></pre>

To then pull data by Author from the table, you use the view's FindRows function...

<pre><code> dataRowViews = _dvChangesByAuthor.FindRows(author);
 List&lt;DataRow&gt; returnRows = new List&lt;DataRow&gt;();
 foreach (DataRowView drv in dataRowViews)
 {
 returnRows.Add(drv.Row);
 }
</code></pre>

I made a random large DataTable, and ran queries using DataTable.Select(), Linq-To-DataSet (with forced execution by exporting to list) and the above DataView method. The DataView method won easily. Linq took 5000 ticks, Select took over 26000 ticks, DataView took 192 ticks...

<pre><code>LOC=20141121-14:46:32.863,UTC=20141121-14:46:32.863,DELTA=72718,THR=9,DEBUG,LOG=Program,volumeTest() - Running queries for author &gt;TFYN_AUTHOR_047&lt;
LOC=20141121-14:46:32.863,UTC=20141121-14:46:32.863,DELTA=72718,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingLinqToDataset() - Query elapsed time: 2 ms, 4934 ticks; Rows=65 
LOC=20141121-14:46:32.879,UTC=20141121-14:46:32.879,DELTA=72733,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingSelect() - Query elapsed time: 11 ms, 26575 ticks; Rows=65 
LOC=20141121-14:46:32.879,UTC=20141121-14:46:32.879,DELTA=72733,THR=9,DEBUG,LOG=RightsChangeTracker,GetChangesByAuthorUsingDataview() - Query elapsed time: 0 ms, 192 ticks; Rows=65
</code></pre>

So, if you want indices on a DataTable, I would suggest DataView, if you can deal with the fact that the index is re-built when the data changes.

I am using VSTS 2008 + C# + .Net 3.5 + SQL Server 2008 + ADO.Net. If I load a table from a database by using a DataTable of ADO.Net, and in the database table, I defined a couple of indexes on the table. My question is, whether on the ADO.Net DataTable, there is related index (the same as the indexes I created on physical database table) to improve certain operation performance on DataTable?

thanks in advance,
George

Do ADO.Net DataTables have indexes?

SQL Server

数据库

我使用的是VSTS2008+ C# + .Net 3.5 + SQL Server2008+ ADO.Net。如果我使用ADO.Net的DataTable从数据库装入一个表，并且在数据库表中，我在该表上定义了两个索引。我的问题是，在ADO.Net DataTable上，是否有相关的索引(和我在物理数据库表上创建的索引一...

问ADO.Net DataTables有索引吗？
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