How to avoid duplicated when merging two tables

I want to merge two tables but I found duplicated IDs in result table dt30.   How to avoid?
Any comment or instruction will be appreciated!!

         //DataTable dt30 = new DataTable();
            //DataTable dt60 = new DataTable();
            //dt30 = ReportsUtility.GetFormExceptionsList(LeftIDs, RightIDs, POHData.DAOs.Reports.DQ.DqFormExceptionsDao.ReportTypes.ThirtyDayExceptions);
            //dt60 = ReportsUtility.GetFormExceptionsList(LeftIDs, RightIDs, POHData.DAOs.Reports.DQ.DqFormExceptionsDao.ReportTypes.SixtyDayExceptions);
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Jacques Bourgeois (James Burger)PresidentCommented:
Your GetFormExceptionList method probably calls Fill to fill the tables. This retrieves the field names and the data, but nothing more.

Have it call FillSchema before calling Fill so that the DataTable knows which field is the PrimaryKey.

You might also look the documentation for the following overload of Merge:

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jssong2000Author Commented:
Thank you!
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