Linq query to update datatable column


I am trying to update a column in a datatable with another datatable column using linq query

Case :
dt1 - there is an empty column - Name
dt2 - column named - Names

Common column for both the tables is Emp ID column

need to update Name column in dt1

Help me with the linq query

Hi @Sasikanth

Welcome to community!

Have you tried Join Datatable?


Sudarsan, this is not going to solve my requirement.

If there is anything that can be done using linq query that would be great

OKay @Sasikanth

Can you share sample input and output here?


Sample input:
dt1 has 10 rows with below columns
Emp ID, Name, Area - out of these Column ‘Name’ is empty

dt2 has 5 rows with below columns
Emp ID, Name, Location

I have to perform left join and need output in the same dt1
dt1 should have same 10 rows with all the columns
Emp ID, Name, Area but only for the matched empIDs in dt2 , Name column in dt1 should be filled

have you checked this video @Sasikanth


i did check this video, since he has done with the same number of rows in both the data tables, it is not the exact solution to my problem. And also the common column values are all matching with both the tables and hence he got all the rows.

But in my case i have less number of rows in dt2 and when i try to execute the query i am only getting the matching rows …rest of my rows in dt1 are not coming

Try to join dt2 to dt1 and check once @Sasikanth

Hi @Sasikanth,

Use below code

dt1=dt1.AsEnumerable().ToList().ForEach(Sub(row) row("Name")= If(dt2.AsEnumerable().Where(Function(r) r("Emp ID").ToString.Equals(row("Emp ID").ToString)).Count<>0, dt2.AsEnumerable().Where(Function(r) r("Emp ID").ToString.Equals(row("Emp ID").ToString))(0)("Name").ToString,row("Name").ToString))


When i try to use the code which you gave @arivu96 getting the below

Error ERROR No compiled code to run
error BC36639: ‘ByRef’ parameter ‘dt2’ cannot be used in a lambda expression. At line 3
error BC36639: ‘ByRef’ parameter ‘dt2’ cannot be used in a lambda expression. At line 4 _Test.xaml

have an introduction on several options for updating a column here:
How to Update Data Column Values of a Data Table | Community Blog

so datatable reconstruction along with left join / LookUp Left:dt1 - Right:dt2) would be one option to solve it

this is nice @ppr . But i am not getting how to implement the logic for my problem

If you can help me with the query or any solution it would be helpful

@ppr - i did see your post below

and tried to implement the same but this query also gives me only matched records

just share sample data along with expected output with us. Thanks

@ppr . PFB


ID Area Name
1 Bangalore
2 Hyd
3 Chennai
4 Pune
5 Gurgaon
6 Kolkata

ID Name
1 Rajesh
2 Suresh
3 Rocky
5 Gopi

Output Dt - Expected Output
ID Name Area
1 Rajesh Bangalore
2 Suresh Hyd
3 Rocky Chennai
4 Pune
5 Gopi Gurgaon
6 Kolkata

let me know if this is fine to solve the problem. Name is the empty column in dt1 that needs to filled with dt2 column values based on the matching ID

We recommend also to study

  • datatable join activity
  • LookUp DataTable activity

One of many options:

Assign Activity:
dtResult = dt1.Clone | Assumption: Colstructure: ID, Area, Name

Assign Activity:
dtResult =

(From d1 In dtData1.AsEnumerable
Group Join d2 In dtData2.AsEnumerable 
On d1("ID").toString.Trim Equals d2("ID").toString.Trim Into gj = Group
From g In gj.DefaultIfEmpty
Select ra = {d1("ID"), d1("Area") ,If(isNothing(g), Nothing, g("Name")) }
Select dtResult.Rows.Add(ra)).CopyToDataTable

dtResult is then the reconstructed DataTable as described as approach in the shared Blog

As an alternate Option you can also create a LookUp Dictionary and use it for the name retrieval.

Hi @ppr ,

I even tried the query you gave, but still its giving me only matched rows in dt1 instead of the whole dt1. Sorry i am bit slow learner if this is bothering you…but i understood the query and implemented the same…still its not giving me the desired output.

Is there any other way we can make a modification in the query because we can actually get this using nested for each but query seems the optimized way and faster…so trying for that

an implementation

done as described above will bring this sample data

to the following:

If the column positions matter then:

  • instead of cloning prepare an empty datatable with the alternae structure AND rearrange the RA construction within the LINQ