Posted on 2013-10-23
Last Modified: 2016-02-10
I have two datatables T1 and T2
I neeed to do a join but only get the first or default from T2
Because T2 could have multiple rows that match the join condition

I tried this
 var result = (from dataRows1 in T1.AsEnumerable()
                            join dataRows2 in T2.AsEnumerable()
                            on dataRows1["ID"] equals dataRows2["ID"]
                            select new Returns
                                ID = dataRows1["ID"],
                                Date = dataRows1["Date"],
                                StartPrice = Convert.ToDecimal(dataRows2["StartPrice"]),
                                EndPrice = Convert.ToDecimal(dataRows2["EndPrice"])

Question by:countrymeister
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LVL 63

Assisted Solution

by:Fernando Soto
Fernando Soto earned 100 total points
ID: 39594749
Hi countrymeister;

You state the following, "I need to do a join but only get the first or default from T2", it is possible the the other lines are getting filtered out because of the use of the Distinct method call in the query. To test remove the Distinct() and leaving everything else in place.

Author Comment

ID: 39594797
I removed the distinct that did not help
t1 has 2550 rows, and T2 has 4890 rows, I just want the 2550 rows back in my join

Example t2 could have multiple rows with ID matching the ID in T1
LVL 63

Expert Comment

by:Fernando Soto
ID: 39594812
How many rows are you getting back?
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Author Comment

ID: 39594822
I am getting 4890 rows back
LVL 63

Expert Comment

by:Fernando Soto
ID: 39594970
I have tried similar Linq query and it seems to work on my systems as expected.

Running the query using the Distinct() method and you tell me the number of records returned?

Also can you post a screen shot of the results where data is missing?
LVL 75

Accepted Solution

käµfm³d   👽 earned 400 total points
ID: 39596299
Add a group by to the mix:


 var result = (from dataRows1 in T1.AsEnumerable()
               join dataRows2 in T2.AsEnumerable()
               on dataRows1["ID"] equals dataRows2["ID"]
               group new { ID = dataRows1["ID"], Date = dataRows1["Date"], StartPrice = dataRows2["StartPrice"], EndPrice = dataRows2["EndPrice"] }
               by dataRows1["ID"] into g
               let first = g.FirstOrDefault()
               let firstDate = (first == null ? (DateTime)null : Convert.ToDateTime(dataRows1["Date"]))
               let firstStartPrice = (first == null ? 0M : Convert.ToDecimal(dataRows2["StartPrice"]))
               let firstEndPrice = (first == null ? 0M : Convert.ToDecimal(dataRows2["EndPrice"]))
               select new Returns
                   ID = g.Key,
                   Date = firstDate,
                   StartPrice = firstStartPrice,
                   EndPrice = firstEndPrice,


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