Someone help me with what went wrong? Thank you very much! The code is as follows:

 
OleDbConnection conn=new OleDbConnection (" Provider=Microsoft. JET. The OLEDB. 4.0; Data Source="+ @" C: \ Temp \ 901. MDB "); 
Conn. The Open (); 

OleDbDataAdapter adapter=new OleDbDataAdapter (" SELECT * FROM OrderTransactions ORDER BY OrderTransactionID ", conn); 

OleDbCommand updateCommand=new OleDbCommand (" UPDATE OrderTransactions SET LastRowHash=? WHERE OrderTransactionID=? ", conn); 

UpdateCommand. The Parameters. The Add (" p1 ", OleDbType VarWChar, 50, "LashRowHash"); 
OleDbParameter param=updateCommand. The Parameters. The Add (" p2 ", OleDbType. Integer); 
Param. SourceColumn="OrderTransactionID"; 
Param. SourceVersion=DataRowVersion. The Original; 

Adapter. UpdateCommand=UpdateCommand; 
The DataTable data=https://bbs.csdn.net/topics/new the DataTable (); 
Adapter. The Fill (data); 

String rowString; 
Foreach (DataRow row in the data. The Rows) 
{
RowString=""; 
Foreach (DataColumn col in the data. The Columns) 
{
If (col) ColumnName) ToUpper ()!="LASTROWHASH") 
{
RowString +=row [col]. ToString (); 
} 
} 

String hashString=ComputeMD5 (rowString); 
If (row [" LastRowHash "]. ToString ()!=hashString) 
{
Row [" LastRowHash "]=hashString; 
} 
} 

Adapter. Update (data); 

Conn. Close ();