How to select and record No duplicates in a DataTable? _null

Just like the SELECT distinct field name from table name
What to do with the select in the DataTable?


Reply to the content "wwwiii520":
Occupy a Sand "" "do not understand LZ meaning

"Ezhuyin":
Public DataTable selectdistinct (String tablename, DataTable SourceTable, String FieldName)
{
DataTable dt = new DataTable (tablename);
Dt. Columns.Add (FieldName, Sourcetable.columns[fieldname). DataType);

Object lastvalue = null;
foreach (DataRow Dr in Sourcetable.select ("", FieldName))
{
if (Lastvalue = NULL | |!) ( Columnequal (Lastvalue, Dr[fieldname]))
{
Lastvalue = Dr[fieldname];
Dt. Rows.Add (New Object[]{lastvalue});
}
}
if (ds!= null)
Ds. Tables.add (DT);
return DT;
}

"Outh24":
It would be nice if you had LINQ ...
If not, there is a stupid way to define another DataTable,
Write a duplicate portion of the current data source into the new DT

"fuda_1985":
Concern.

"SCJYJL":
Did not find columnequal, I would like to have a using what this ah, and I have no index in MSDN, you can tell?

"Ezhuyin":
Idea: First create a temporary data table, then sort the source DataTable, and then read the source data line-by-row, and compare it to the last time you added it, and if it is the same, add it to the temporary table if it is the same. Make a small change, you can adapt to more environment.

Public DataTable selectdistinct (String tablename, DataTable SourceTable, string[] fieldnames)
{
DataTable dt = new DataTable (tablename);
System.Text.StringBuilder Filednamebuilder = new System.Text.StringBuilder ("");
String sortstr = "";

foreach (String FieldName in FieldNames)
{
Dt. Columns.Add (FieldName, Sourcetable.columns[fieldname). DataType);
Filednamebuilder.append (FieldName + ",");
}

if (filednamebuilder.tostring (). LENGTH>0)
{
Sortstr = Filednamebuilder.tostring ();
Sortstr = sortstr.substring (0,sortstr.length-1);
}

object[] Lastvalue = new Object[fieldnames.length];

foreach (DataRow Dr in Sourcetable.select ("", Sortstr))
{
if (Lastvalue = NULL | |!) IsEqual (Dr,lastvalue))
{
for (int i = 0; i < lastvalue.length; i++)
{
Lastvalue[i] = dr[fieldnames[i]];
}
Dt. Rows.Add (Lastvalue);
}
}
if (ds!= null)
Ds. Tables.add (DT);
return DT;
}

private bool IsEqual (DataRow Dr, object[] Value)
{
bool Equal = true;
int current = 0;

while (Equal && current < Value.length)
{
if (!dr[current). Equals (Value[current])
{
Equal = false;
}
Else
{
current++;
}
}

return Equal;
}

"Ezhuyin":
Did not find columnequal, I would like to have a using what this ah, and I have no index in MSDN, you can tell?

Ah, sorry, that's a separate method:

private bool Columnequal (object A, Object B)
{
if (a = = DBNull.Value && B = dbnull.value)//two are DBNull.Value
return true;
if (A = = DBNull.Value | | B = = DBNull.Value)//Only one is DBNull.Value
return false;
Return (A.equals (B)); Normal comparison
}

"Ezhuyin":
if (!dr[current). Equals (Value[current])

Another mistake, modified into

if (! Columnequal (Dr[current],value[current])

"SCJYJL":
Thanks, Ezhuyin.