Question

我有一个winform，其中用户通过组合框输入值。我正在为搜索db分配组合框值。如果没有选择，那么SQL服务器查询不应该使用该列进行过滤。

示例 -

if (string.IsNullOrEmpty(combobox1.text)) {
  .....Select * from country
}
else if (combobox1.selectedindex > -1) {
   ....Select * from country where city_name = combobox.text
}

有没有办法编写单个查询，而不是使用此多个＆＃39; IF＆＃39;用户选择或不从组合框中选择值的情况。

Answer 1

同样重要的是参数化：

private const string _select = "select * from country";

void DoSomething()
{
     string sql = string.Empty;
     if (combobox1.SelectedIndex > -1)
     {
         command.Parameters.AddWithValue("@1",  (string)combobox1.SelectedValue);
         sql = " where city_name = @1";
     }
     sql = _select + sql;
     command.CommandText = sql;
     command.Execute...
}

@ un-lucky问我怎么处理很多条件 - 这是一种方式

var conditions = new List<string>();     
if (/* condition 1*/)
{
    command.Parameters.AddWithValue("@2",  (string)cboN.SelectedItem);
    conditions.Add("col1 = @2");
}
if (/* condition 2*/)
{
    command.Parameters.AddWithValue("@3",  textBoxN.Text);
    conditions.Add("col2 = @3");
}

if (conditions.Count > 0)
    sql = _select + " where " + string.Join(" AND ", conditions.ToArray());

Answer 2

如果您有两个条件，则可以使用速记：

 string query = string.Format("Select * from country{0}", string.IsNullOrEmpty(combobox1.text) ? "" : " where city_name = " + combobox1.text);

希望它有所帮助！

Answer 3

我认为你必须尝试使用参数化：

StringBuilder queryBuilder = new StringBuilder("Select * from country Where 1=1 ");
SqlCommand cmdSql = new SqlCommand();

if (combobox1.selectedindex > -1) 
{
   queryBuilder.Append(" And city_name = @city_name "); 
   cmdSql.Parameters.Add("@city_name", SqlDbType.VarChar).Value = combobox.text;  
}
else if(Condition 2)
{
   queryBuilder.Append(" And column2 = @col2 "); 
   cmdSql.Parameters.Add("@col2", SqlDbType.VarChar).Value = "some Value here;  
}
// Build the query like this
cmdSql.CommandText= = queryBuilder.ToString();
cmdSql.Connection = conObject;
// Here you can execute the command

Answer 4

我有一个样本，试试吧

string select = this.combobox1.GetItemText(this.combobox1.SelectedItem); cm1 = new SqlCommand("Select * from country where city_name=@select or @select is null", con);
            cm1.Parameters.Add("@select", SqlDbType.NVarChar, 50);
            cm1.Parameters["@select"].Value = select;
            dap = new SqlDataAdapter(cm1);
            ds = new System.Data.DataSet();
            dap.Fill(ds, "DATABASE");
            //DataGridView1.DataSource = ds.Tables[0]; get data

如何根据组合框选择编写单个sql查询？

4 个答案: