如何比较不同数据表中的2列

Question

table1

id  | fileName   |  fileDateTime
1   | somefile   |  somedatetime
2   | somefile2  |  somedatetime2

table2

id   |   fileName    |   fileDateTime
     |   somefile1   |   somedatetime1
     |   somefile2   |   somedatetime2

output table3

id   |   fileName    |    fileDatetime
     |   somefile1   |    somedatetime1

I want to compare the 2 tables (column 2 & 3 only) and only have what is not in both tables, there is no ID field in the 2nd table. Then I plan on parsing the data in the file and add file info to database to record file has been parsed. I am having trouble comparing the 2 fields. This does not seem to work.

for (int i = 0; i < finalTable.Rows.Count; i++)
{
    for (int r = 0; r < filesTable.Rows.Count; i++)
    {
        if (finalTable.Rows[i][2] == filesTable.Rows[r][2])
        {
            finalTable.Rows.Remove(finalTable.Rows[i]);
        }
    }
}

Answer 1

Assuming the value is a string, you could just do

for (int i = 0; i < finalTable.Rows.Count; i++)
{
    for (int r = 0; r < filesTable.Rows.Count; i++)
    {
        if (finalTable.Rows[r].Field<string>(2) == filesTable.Rows[r].Field<string>(2))
        {
            finalTable.Rows.Remove(finalTable.Rows[i]);
        }
    }
}

If it's another type, just change the <string> for the real type !

Answer 2

You can use Linq to achieve it as shown below.

Assuming your fields are string. For other datatype you can cast them accordingly:

using System.Data.Linq;
......
......
// Merge both tables data and group them by comparing columns values
dt1.Merge(dt2); 
var g = dt1.AsEnumerable()
        .GroupBy(x => x[0]?.ToString() + x[1]?.ToString()) // You can build Unique key here, I used string concatination
        .ToDictionary(x => x.Key, y => y.ToList());

var unique = dt1.Clone();

foreach (var e in g)
{
    if (e.Value.Count() == 1) // In either table - Intersaction 
    {
        e.Value.CopyToDataTable(unique, LoadOption.OverwriteChanges);
    }

    if (e.Value.Count() == 2) 
    {
        // In both tables -Union
    }
}