如何根据另一个表删除一个表中的行？

Question

I have a table1 with datarows that I would like to remove from table2. I tried to loop thru the data and remove accordingly...

while (myDataReader.Read())
{        
    DataTable.Rows.Remove(DataRow);
}

no luck, I also tried to remove after the two tables have been populated

var correctDataTable = from p in DataTable
                      where (!tempDataTable.Rows.Contains(p))
                      select new { p };

Any ideas?

Answer 1

I would write a query to do it all in one statement

delete from TableA
where ColID in (select colid from tableB)

Answer 2

Remove all records from dtCMATM table that are not in dtAllowedList table.

     private void GetProperData()
   {
        DataTable dtAllowedList = someclass.somefunctiontogetdata(....);
        DataTable dtCMATM = someclass.somefunctiontogetdataTobeRemovedLaterOn(.........);
        DataTable tblCloned = new DataTable();
        tblCloned = dtCMATM.Clone();

        foreach (DataRow dr2 in dtAllowedList.Rows)
        {
        DeleteRowsFromDataTable(ref tblCloned, dtCMATM, "AssignTo", dr2[0].ToString());
        }

        tblCloned.AcceptChanges();
        dtCMATM = tblCloned;
        dtCMATM.AcceptChanges();    

   }

    private static void DeleteRowsFromDataTable(ref DataTable tblCloned, DataTable dtCMATM, string ColumnName, string columnValue)
    {           
        string strExpression = "AssignTo = '" + columnValue + "' ";
        dtCMATM.DefaultView.RowFilter = strExpression;
        dtCMATM = dtCMATM.DefaultView.ToTable();

        if (dtCMATM.Rows.Count > 0)
        {
            tblCloned.ImportRow(dtCMATM.Rows[0]);
        }           
    }    

Answer 3

Hold on

 DataTable.Rows.Remove(DataRow); 

will not actually remove the data in your database, supposing this is what you want. This way you only remove rows from a rows collection in you datatable object.

Next step is to actually commit the changes to the database. Again, supposing this is what you are looking for.

Answer 4

What do you mean to remove? Can you please specify a bit better what would you like to to? To remove the whole row from the table, or only one cell? - based on what? Your 1st post is very unclear.

So you have two tables. 1st one has ALL the data, the 2nd one has some. And if any data from table2 exists in table1, these data from table 1 has to be removed? Am I right?

You can loop through the rows of both tables (so double loop):

foreach (DataRow dr1 in table1.Rows)
        {
            foreach (DataRow dr2 in table2.Rows)
            {
                if (dr1[0].ToString() == dr2[0].ToString())
                {
                    table1.Rows.Remove(dr1);
                    break;
                }
            }
        }

Answer 5

I figured it out. I added the following to my while loop for table2(table with rows to be removed).

while (myDataReader.Read())
{
     DataRow drNew = DataTable.NewRow();
     drNew["ID"] = myDataReader["ID#"].ToString().Trim();
     drNew["Name"] = myDataReader["NAME"].ToString().Trim());
     ...
     DataRow[] badRow = DataTable.Select(
          "ID='" + drNew["ID"] + "' and Name='" + drNew["Name"] + "'");
     if(badRow.Length >0)
         DataTable.Rows.Remove(badRow[0]);
}

Answer 6

If what you want is to delete some rows from a dataTable using a key stored in another dataTable you can iterate the table with the keys, find the key in the table where you want to delete and …done.

Example:

Consider TABLE2 with (table1ID, col2, col3, col4) columns and TABLE1 with (id, col2, col3) columns. You can do:

foreach (TABLE2row t2r in TABLE2)
{
    t1r=TABLE1.FindByID(t2r.Table1ID);
    if (t1r!=null) 
    {
        t1r.delete();
    }
}

This is considering that you use Typed datasets with primary keys.