DataView RowFilter Syntax [C#]

RowFilter语法

         private void btnEnquiry_Click(object sender, EventArgs e)
         {
             string filterExpression = string.Empty;
             //filter QCPass
             if (cbbQCPass.SelectedIndex !=  && cbbQCPass.SelectedIndex != -)
             {
                 string qcPassRowFilter = string.Format("qcpass = {0}", cbbQCPass.SelectedItem);
                 filterExpression += qcPassRowFilter;
             }
             //filter epc
             if (!string.IsNullOrWhiteSpace(txtEPC.Text))
             {
                 if (!string.IsNullOrEmpty(filterExpression))
                 {
                     filterExpression += " AND ";
                 }
                 string epcFilter = string.Format("epc like '%{0}%'", txtEPC.Text.Trim());
                 filterExpression += epcFilter;
             }
             //filter seq
             if (!string.IsNullOrWhiteSpace(txtSEQ.Text))
             {
                 if (!string.IsNullOrEmpty(filterExpression))
                 {
                     filterExpression += " AND ";
                 }
                 string seqFilter = string.Format("seq like '%{0}%'", txtSEQ.Text.Trim());
                 filterExpression += seqFilter;
             }

             if (!string.IsNullOrEmpty(filterExpression))
             {
                 _dataSource.DefaultView.RowFilter = filterExpression;
             }
             else
             {
                 _dataSource.DefaultView.RowFilter = string.Empty;
             }
         }