Update not working in gripview using asp.net

<asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
            AutoGenerateColumns="False" DataKeyNames="SRNO" DataSourceID="shift">
            <columns>
                <asp:BoundField DataField="SRNO" HeaderText="SRNO" ReadOnly="True" 
                    SortExpression="SRNO" />
                <asp:CommandField ShowEditButton="True" />
                <asp:BoundField DataField="LOCATION" HeaderText="LOCATION" 
                    SortExpression="LOCATION" />
                <asp:BoundField DataField="NAT_WORK" HeaderText="NAT_WORK" 
                    SortExpression="NAT_WORK" />
                <asp:BoundField DataField="TARGETDATE" HeaderText="TARGETDATE" 
                    SortExpression="TARGETDATE" />
                <asp:BoundField DataField="WORKPROG" HeaderText="WORKPROG" 
                    SortExpression="WORKPROG" />
                <asp:BoundField DataField="DONEBY" HeaderText="DONEBY" 
                    SortExpression="DONEBY" />
                <asp:BoundField DataField="DONEON" HeaderText="DONEON" 
                    SortExpression="DONEON" />
                <asp:BoundField DataField="READY" HeaderText="READY" SortExpression="READY" />
                <asp:BoundField DataField="SHOW" HeaderText="SHOW" SortExpression="SHOW" />
            </columns>
        
        <asp:SqlDataSource ID="shift" runat="server" 
            ConnectionString="<%$ ConnectionStrings:constr %>" 
            ProviderName="<%$ ConnectionStrings:constr.ProviderName %>" 
            SelectCommand="SELECT * FROM "GMOSHIFT"" 
            InsertCommand="INSERT INTO "GMOSHIFT" ("SRNO", "LOCATION", "NAT_WORK", "TARGETDATE", "WORKPROG", "DONEBY", "DONEON", "READY", "SHOW") VALUES (:SRNO, :LOCATION, :NAT_WORK, :TARGETDATE, :WORKPROG, :DONEBY, :DONEON, :READY, :SHOW)">
            <insertparameters>
                <asp:Parameter Name="SRNO" Type="Decimal" />
                <asp:Parameter Name="LOCATION" Type="String" />
                <asp:Parameter Name="NAT_WORK" Type="String" />
                <asp:Parameter Name="TARGETDATE" Type="String" />
                <asp:Parameter Name="WORKPROG" Type="String" />
                <asp:Parameter Name="DONEBY" Type="String" />
                <asp:Parameter Name="DONEON" Type="String" />
                <asp:Parameter Name="READY" Type="String" />
                <asp:Parameter Name="SHOW" Type="String" />
            </insertparameters>