如何从sql数据库中检索asp.net mvc中的行数？

Question

如果基于查询返回的行数大于 0，我正在尝试打印一些内容：

using (SqlConnection con = new SqlConnection("ConnectionString")){
  con.Open();
  string query = "SELECT COUNT(*) FROM Some_Table WHERE Val > 5";
  SqlCommand cmd = new SqlCommand(query, con);
  cmd.ExecuteNonQuery(); // get the value of the count
  if (count > 0) 
  {
    Console.WriteLine("Returned more than 0 rows");
  }
  else
  {
    Console.WriteLine("Did not return more than 0 rows");
  }
  Console.ReadLine();
}

如何找到返回的行数？

Answer 1

即使不存在任何行，您的查询也始终返回一行。如果您的 WHERE 条件不存在任何行，它将返回 0

使用SqlCommand.ExecuteScalar Method ()

using (var con = new SqlConnection("ConnectionString"))
{
  con.Open();
  string query = "SELECT COUNT(*) FROM Some_Table WHERE Val > 5";

  using (var cmd = new SqlCommand(query, con))
  {
      int rowsAmount = (int)cmd.ExecuteScalar(); // get the value of the count
      if (rowsAmount > 0) 
      {
          Console.WriteLine("Returned more than 0 rows");
      }
      else
      {
          Console.WriteLine("Did not return more than 0 rows");
      }

      Console.ReadLine();
}

ScalarValue 将返回查询结果第一行的第一列。因此，对于您的查询，这是检索所需信息的更有效方法。

Answer 2

您可以这样做，因为ExecuteNonQuery - 返回受影响的行数。

int numberOfRecords = cmd.ExecuteNonQuery();
if (numberOfRecords  > 0) 
{
  Console.WriteLine("Returned more than 0 rows");
}
else
{
    Console.WriteLine("Did not return more than 0 rows");
}

Answer 3

SQLClient Command 对象的 ExecuteScalar() 方法专门用于从查询中返回单个值。它在代码和性能方面更高效。

using (SqlConnection conn = new SqlConnection("ConnectionString"))
{
conn.Open();
string query = "SELECT COUNT(*) FROM Some_Table WHERE Val > 5";
SqlCommand command = new SqlCommand(query, con);
Int32 count = (Int32) cmd.ExecuteScalar()
}

Answer 4

使用DataSet 获取计数

SqlCommand cmd = new SqlCommand(query, con);

SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
DataSet ds = new DataSet();

da.Fill(ds);

var count = ds.Tables[0].Rows.count;