无法在 SQL Server 2008 中使用 where 子句获取 nvarchar 类型数据

Question

string constr = Properties.Settings.Default.Subject_1ConnectionString;

SqlConnection conn = new SqlConnection(constr);
SqlCommand com = new SqlCommand("SELECT * from Subject_Title WHERE Date BETWEEN @hello and @hello1 ", conn);

// com.Parameters.Add("@hello", SqlDbType.NVarChar).Value = textBox1.Text;
// com.Parameters.Add("@hello1", SqlDbType.NVarChar).Value = textBox2.Text;

com.Parameters.Add("@hello", SqlDbType.NVarChar);
com.Parameters["@hello"].Value = textBox1.Text;

com.Parameters.Add("@hello1", SqlDbType.NVarChar);
com.Parameters["@hello1"].Value = textBox2.Text;

// com.Parameters.AddWithValue("@hello", textBox1.Text);
// com.Parameters.AddWithValue("@hello1", textBox2.Text);
SqlDataAdapter da = new SqlDataAdapter(com);
DataSet ds = new DataSet();
da.Fill(ds, "Subject_title");

for (int i = 0; i < 8; i++)
{
    this.labeltext = this.labeltext + " " + ds.Tables["Subject_Title"].Rows[i]["Date"].ToString();
    this.labeltext = this.labeltext + " " + ds.Tables["Subject_Title"].Rows[i]["Subject"].ToString();
    this.labeltext = this.labeltext + " ";
}

this.label1.Text = this.labeltext;

这里我没有从数据库中获取任何数据

Date 是我的列名，具有 nvarchar 类型，Subject 是另一个类型为 text 的列。

请大家解决我的问题

Answer 1

我猜你应该使用： Con.Open(); Con.Close();

但如果我是你，我会这样写代码：

    string constr = Properties.Settings.Default.Subject_1ConnectionString;

    SqlConnection conn = new SqlConnection(constr);
    SqlCommand com = new SqlCommand("SELECT * from Subject_Title WHERE Date BETWEEN \"01-03-14\" and \"01-04-14\" ", conn);

    conn.Open();       
    SqlDataReader reader =com.ExecuteReader();
    while(reader.read()){

    this.labeltext += " " + reader.GetString(0);       //Use column ordinal for Date
    this.labeltext += " " + reader.GetString(1)+" ";   //Use column ordinal for Subject
    }
    conn.Close()
    this.label1.Text = this.labeltext;

Answer 2

我试图为你想出一个更好的代码库。

你需要：

• 使用更有意义的名称！ hello 和 hello1 之类的参数对于阅读您的代码的人来说不是很有用....另外：不要使用保留关键字命名您的列，例如 Date - 再次：使用对您的上下文更有意义的东西

• 如果要使用与日期相关的方法，则必须使用DATE 或DATETIME2(N) 数据类型。如果您已将数据存储为 nvarchar - 您必须先将其转换为 DATE

• 请始终将您的 SqlConnection 和 SqlCommand 放入 using(...) { .. } 块中，以确保正确快速地处理

• 如果您只需要一个 DataTable - 只需实例化一个 DataTable 并填充它 - 不要使用 DataSet 的不必要的额外开销 - 那只是浪费资源......

代码：

string constr = Properties.Settings.Default.Subject_1ConnectionString;

// if you only need one single data table - use a DataTable - not a DataSet !
DataTable dt = new DataTable();

// *ALWAYS* put your SqlConnection and SqlCommand into using() blocks!
// also - if you want to use BETWEEN, you *MUST* use DATE!
// also: don't call your column "date" - that's a SQL Server reserved keyword! Use a more meaningful name 
// like "DateCreated" or "DateLastUpdated" or something
// and please also use more meaningful parameter names - "hello" and "hello1" is very confusing and not clear!!
using (SqlConnection conn = new SqlConnection(constr))
using (SqlCommand com = new SqlCommand("SELECT * FROM dbo.Subject_Title WHERE CAST(DateCreated AS DATE) BETWEEN @start and @end ", conn))
{
   // add parameters as DATE type!
   com.Parameters.Add("@start", SqlDbType.Date);
   com.Parameters["@start"].Value = DateTime.Parse(textBox1.Text).Date;

   com.Parameters.Add("@end", SqlDbType.Date);
   com.Parameters["@end"].Value = DateTime.Parse(textBox2.Text).Date;

   SqlDataAdapter da = new SqlDataAdapter(com);

   da.Fill(dt);
}

for (int i = 0; i < 8; i++)
{
    this.labeltext = this.labeltext + " " + dt.Rows[i]["Date"].ToString();
    this.labeltext = this.labeltext + " " + ds.Rows[i]["Subject"].ToString();
    this.labeltext = this.labeltext + " ";
}

this.label1.Text = this.labeltext;