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query datable

Posted on 2013-11-11
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Last Modified: 2013-11-12
Is there a way to query datatable in vb.net?
sample I have datatable contains 500 row. column one is called "client_req_id".  I want to do like select distinct(client_req_id) from my datatable.
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Question by:VBdotnet2005
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LVL 62

Expert Comment

by:Fernando Soto
ID: 39640616
Hi VBdotnet2005;

The Linq query language can be used to query a DataTable object. If you give more information on the columns and what you wish to filter the table on and what you want the result set to look like we may be able to come up with some sample code.
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Author Comment

by:VBdotnet2005
ID: 39640806
FernandoSoto,

sample datatable - I just want to find out a list for distinct(client_req_id ).

client_req_id     zipcode
78001                90001
78002                90002
78001                90003
78005                90002
etc

result would be

78001
78002
78005
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LVL 69

Expert Comment

by:Éric Moreau
ID: 39641269
The ToTable method of the DataView object let you do it: http://msdn.microsoft.com/en-us/library/wec2b2e6(v=vs.110).aspx

I posted another link yesterday containing an example but apparently it was removed!
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LVL 62

Expert Comment

by:Fernando Soto
ID: 39642621
Hi VBdotnet2005;

The following code snippet will iterate through your DataTable objects and return a List(Of Integer) with distinct values only.

Dim results = (From r In dt.AsEnumerable() _
               Order By r.Field(Of Integer)("client_req_id") _
               Select r.Field(Of Integer)("client_req_id")).Distinct().ToList()
               
' Where dt is the named instance of a DataTable object  

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Author Comment

by:VBdotnet2005
ID: 39642718
Okay. That works for me. Since this is LINQ, I hope you don't mind,  how can I query selected fields (field1, field2, field3). I don't need it to return every column.


Dim results = (From r In dt.AsEnumerable() _
               where (f.field(of string)("client_req_id") = "BOFA_101"
             select filed1, field2, field3      <<<<<<<<

I want to copy Results to a different datatable.
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LVL 62

Expert Comment

by:Fernando Soto
ID: 39642802
Hi VBdotnet2005;

In the select start each field with a VB variable name the = then the Field to return followed by a comma. Continue this until you have identified all columns to be returned as shown in the code snippet below.

Dim results = (From r In dt.AsEnumerable() _
               Where r.Field(of String)("client_req_id") = "BOFA_101" _
               Select _
                   client_req_id = r.Field(of String)("client_req_id"), _
                   zipcode = r.Field(of String)("zipcode"), _
                   ' VariableName = r.Field(Of DataType)("String Column Name") _
                   ' All remaining fields here as above _
              )

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Author Comment

by:VBdotnet2005
ID: 39642915
Can I convert results  to datatable?
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LVL 62

Accepted Solution

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Fernando Soto earned 500 total points
ID: 39642954
There is no function to convert the results into a DataTable object. If the DataTable already exists then it is just a matter of getting a blank row from that DataTable object using the DataTableInstance.NewRow() method and assigning the values the that row and then adding that NewRow back to the DataTable by using DataTableInstance.Rows.Add(TheNewRow). If the DataTable does not exist Create a DataTable and create a new DataColumn object for each column and adding those column to the DataTable object using DataTableInstance.Columns.Add(NewColumn). Once you have that you can follow the instructions above for when you have an existing table.
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Author Comment

by:VBdotnet2005
ID: 39643205
Please see this link as a sample. I am not sure why I can't just select the column I need from a table and return it as a table.

http://matijabozicevic.com/blog/csharp-net-development/csharp-using-linq-to-query-datatable

var movies = from p in dtMovies.AsEnumerable()
             where p.Field<int>("Year") >= 1995
             select new
             {
                 ID = p.Field<int>("ID"),
                 Title = p.Field<string>("Title"),
                 Year = p.Field<int>("Year")
             };
 
 
// Writing some output...
foreach (var movie in movies)
{
    Console.WriteLine(string.Format("{0}. {1}  ({2})", movie.ID, movie.Title, movie.Year));
}


---


Dim results = From r In dt.AsEnumerable() _
               Where r.Field(of String)("client_req_id") = "BOFA_101" _
               Select  new {
                   client_req_id = r.Field(of String)("client_req_id"), _
                   zipcode = r.Field(of String)("zipcode")
                  }
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Author Closing Comment

by:VBdotnet2005
ID: 39643432
i got it. Thank you
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