Why OLEDB for oracle does not work?

When Accessing Oracle Database using OleDb, I added a ";" in sql command,

string sqlCommandText="select * from tbllog；";

And I debugged it for 2 hours in the night. Later through analysis of programs written several days ago, I found that the sql statement with a ";" in the end would not work.

Thus I delete the ";", however, it still does not work using OleDb. I am confused.

The following is testing codes, the codes commented use the OleDb to access oracle database, and failed. The codes using OralceConnection of System.Data.OracleClient just do the work.

            string connectionString=
                System.Configuration.ConfigurationSettings.AppSettings["ConnectionString"];

            string sqlCommandText="select * from tbllog";

            //here it is the failed solution using OleDB: 
            //should add "using System.Data.OleDb;" in the head 
//            string oleConnectionStr="Provider=OraOLEDB.Oracle;Data Source=OracleSID;User ID=UserID;Password=UserPass";
//            OleDbConnection connection=new OleDbConnection();
    
//            connection.ConnectionString=oleConnectionStr;
//
//            OleDbCommand dbCommand=new OleDbCommand(sqlCommandText,connection);

//            OleDbDataAdapter da=new OleDbDataAdapter();
//            da.SelectCommand=new OleDbCommand(sqlCommandText,connection);
                        

            //Here's the successful solution using OracleClient:
            //Should add reference of System.Data.OracleClient, 
            //and add "using System.Data.OracleClient;" in the head of .cs file
            OracleConnection oOracleConn = new OracleConnection(connectionString);
            OracleDataAdapter da=new OracleDataAdapter();
            da.SelectCommand=new OracleCommand(sqlCommandText,oOracleConn);    

            
            //to fill data to DataSet from Data Adapter
            DataSet ds=new DataSet();
            da.Fill(ds,"tblLog");

            //to display data in table "tblLog"
            DataGrid1.DataSource=ds.Tables[0].DefaultView;
            DataGrid1.DataBind();