SQL查询未获取所有数据C＃/ ASP.net

Question

My SQL-query is not getting information from multiple columns. For testing I'm trying with 2, but I also tried getting all the data, both times it only gives me the first column it finds.

string connectionString = SqlDataSource1.ConnectionString;
SqlConnection connection = new SqlConnection(connectionString);
string insert = "SELECT [ProductName], [productSpace]  FROM [Products] WHERE [ProductId] = '" + NoDupes[z] + "'";

SqlCommand cmd1 = new SqlCommand(insert, connection); 
cmd1.Connection.Open();
Response.Write(cmd1.ExecuteScalar().ToString());

cmd1.Connection.Close();

Answer 1

From SqlCommand.ExecuteScalar method

Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

If you want to return multiple values from your query, you need to use ExecuteReader method .

It is not clear what you want to write but as an example;

using(SqlDataReader reader = cmd1.ExecuteReader())
{
    while (reader.Read())
    {
        Response.Write(reader[0].ToString()); //This writes first column values for your all rows.
    }
}

SqlDataReader.Read method reads your query result rows by rows .

You should use using statement to dispose your SqlConnection and SqlCommand as I did for SqlDataReader . Like;

using(SqlConnection connection = new SqlConnection(connectionString))
using(SqlCommand cmd1 = connection.CreateCommand())
{
    ...
    ...
    connection.Open();
    using(SqlDataReader reader = cmd1.ExecuteReader())
    {
        while (reader.Read())
        {
            Response.Write(reader[0].ToString()); //This writes first column values for your all rows.
        }
    }
}

And more important, you should always use parameterized queries . This kind of string concatenations are open for SQL Injection attacks.

For example;

string insert = @"SELECT ProductName, productSpace FROM Products
                  WHERE ProductId = @id";
SqlCommand cmd1 = new SqlCommand(insert, connection);
cmd1.Parameters.AddWithValue("@id", NoDupes[z]);

As a final tip, you don't need to use square brackets [] for your all column or table names. Use it if your database object name is reserved keyword or contain white space (of course both are not recomended).

Answer 2

You need to use ExecuteReader and iterate through datareader

using (var dr= cmd.ExecuteReader())
    {
        while(dr.Read())
        {
            //Logic
        }
    }

Answer 3

ExecuteScalar executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

Answer 4

if u use

ExecuteScalar():

will work with Non-Action Queries that contain aggregate functions. Return the first row and first column value of the query result. Return type is object. Return value is compulsory and should be assigned to a variable of required type.

ExecuteReader():

will work with Action and Non-Action Queries (Select) Returns the collection of rows selected by the Query. Return type is DataReader. Return value is compulsory and should be assigned to an another object DataReader.

SqlDataReader rdr= cmd1.ExecuteReader();
while (rdr.read())
{  
 Response.Write(rdr.GetValue().ToString().Trim());

}

Answer 5

try this

SqlDataReader reader = cmd1.ExecuteReader();
while (reader.Read())
{
     Response.Write((String.Format("{0}", reader[0]));
}