你可以重新检查你的代码

can you recheck your code

where Stock_Take.Username = '" + DropDownList1.SelectedValue + "' AND Stock_Take.StockDate = '" + DropDownList1.SelectedValue + "'"

我认为Stockdate和用户名的值不应该是相同。

I think the value of Stockdate and username should not be same.

尝试使用Update中的网格视图来更新基于其他控件的内容。

Try to use Grid View in Update to update content based on other controls.