Question

我将如何创建一个可以充当where子句的字符串？ 目前，我做这样说：

string strquery = "select * from tbl_DR_data "; 
string strq2 = "where [Year 1]='" + DropDownList1.SelectedItem.Text + "'and Product='" + DropDownList2.SelectedItem.Text + 
       "'and Media='" + DropDownList3.SelectedItem.Text + "'and Publication='" + DropDownList4.SelectedItem.Text + "'and Genre='" + DropDownList5.SelectedItem.Text + 
       "'and Month='" + DropDownList6.SelectedItem.Value + "'and Section='" + DropDownList7.SelectedItem.Text + "'"; 
string str3 = strquery + strq2; 

但问题是，所有的下拉列表中必须有内它们的值。 我希望能够根据什么下拉有一个值在init中创建一个where语句。因此，例如DDL1和DDL4具有值，但不包括所有其他下拉列表。

我该怎么去做这个？

Answer 1

string strq2 = "where '"; 
if(!string.IsNullOrEmpty(DropDownList1.SelectedItem.Text)) 
strq2 = strq2 + "[Year 1]='" + DropDownList1.SelectedItem.Text + " and "; 
if(!string.IsNullOrEmpty(DropDownList2.SelectedItem.Text)) 
strq2 = strq2 + "Product='" + DropDownList2.SelectedItem.Text+ " and "; 
if(!string.IsNullOrEmpty(DropDownList3.SelectedItem.Text)) 
strq2 = strq2 + "Media='" + DropDownList3.SelectedItem.Text+ " and "; 
if(!string.IsNullOrEmpty(DropDownList4.SelectedItem.Text)) 
strq2 = strq2 + "Publication='" + DropDownList4.SelectedItem.Text+ " and "; 
if(!string.IsNullOrEmpty(DropDownList5.SelectedItem.Text)) 
strq2 = strq2 + "Genre='" + DropDownList5.SelectedItem.Text+ " and "; 
if(!string.IsNullOrEmpty(DropDownList6.SelectedItem.Value)) 
strq2 = strq2 + "Month='" + DropDownList6.SelectedItem.Value+ " and "; 
if(!string.IsNullOrEmpty(DropDownList7.SelectedItem.Value)) 
strq2 = strq2 + "Section='" + DropDownList7.SelectedItem.Value+ " and "; 
strq2 = strq2.Remove(strq2.Length - 5); 

Answer 2

你也许可以格式化你的选择查询作为 -

select * from tbl_DR_data 
where 
ISNULL([YEAR 1], 'X') = ISNULL(DropDownList1.SelectedItem.Text, 'X') 
AND ISNULL(Product, 'X') = ISNULL(DropDownList2.SelectedItem.Text , 'X') 
AND ... so on. 

这样一来，如果选择任何值，则wher条款的那部分将永远是正确的。

Answer 3

你必须学习和使用SqlParameter对象..

string strq2 = "WHERE 1=1"; 
if(!string.IsNullOrEmpty(DropDownList1.SelectedItem.Text)) 
strq2 += " AND [Year 1]=@Year1"; 
if(!string.IsNullOrEmpty(DropDownList2.SelectedItem.Text)) 
strq2 += " AND [Product]=@Product"; 
if(!string.IsNullOrEmpty(DropDownList3.SelectedItem.Text)) 
strq2 += " AND [Media]=@Media"; 
if(!string.IsNullOrEmpty(DropDownList4.SelectedItem.Text)) 
strq2 += " AND [Publication]=@Publication"; 
if(!string.IsNullOrEmpty(DropDownList5.SelectedItem.Text)) 
strq2 += " AND [Genre]=@Genre"; 
if(!string.IsNullOrEmpty(DropDownList6.SelectedItem.Value)) 
strq2 += " AND [Month]=@Month"; 
if(!string.IsNullOrEmpty(DropDownList7.SelectedItem.Value)) 
strq2 += " AND [Section]=@Section";