如何将SQL结果保存到C＃变量中？

Question

I have troubles finding out how to save an SQL result into a String or whatever type the result returns.

My SQL query is:

SELECT SUM(Length) FROM tbl_test WHERE TITLE LIKE 't%'

Here I need a function that sums up the length of all data-rows where title begins with the letter "T", when executing the query in MS-SQL it returns "188.99" (the SQL type is decimal)

My question is, how do I get to save that value into a C# variable? The query always returns ONE row with the particular value, which I want to save into a variable. I have a C# function to execute the query, I just need the value from that row, 188.99, to be saved into a variable. Any suggestions are cool, no matter if I the result is saved into a decimal variable or string.

Answer 1

Try calling .ExecuteScalar() on the SqlCommand that you prepare for it. EG:

SqlConnection connection = new SqlConnection(myConnectionString);
SqlCommand cmd = connection.CreateCommand();
cmd.CommandText = "SELECT SUM(Length) FROM tbl_test WHERE TITLE LIKE 't%'";

int result = ((int)cmd.ExecuteScalar());
connection.Close();

You can open and close SqlConnections as much as you like (it's SoP to open and close each time you do an operation, or series of ops in the same method) because .Net will not really close the connection for real, it'll "soft close" it and plop the live connection back into a Connection Pool for recycling later.

Answer 2

You can use SqlDataReader . Here is a sample :

SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["dbConnectionString"].ToString());


SqlCommand read_command = new SqlCommand("SELECT SUM(Length) FROM tbl_test WHERE TITLE LIKE '@t%'", con);
        read_command.Parameters.Add("@t", SqlDbType.NVarChar).Value = Str;
        SqlDataReader read_rd;
        string SUM ;
        try
        {
            con.Open();
            read_rd = read_command.ExecuteReader();
            if (read_pass_rd.HasRows)
            {
                while (read_rd.Read())
                {
                    SUM = read_rd.GetString(0);
                }
            }
            read_rd.Close();
            con.Close();
        }
        catch (Exception)
        {
            if (con.State == ConnectionState.Open)
                con.Close();
        }

and the 'Str' is a string is the string that you search for, and 'SUM' string is the answer.

Answer 3

You need to connect C# to your Database through some of the available methods:

1. LinQ to SQL
2. ADO.NET
3. LinQ to Entities

I would think ADO.NET is the most basic and straightforward way to do it given you actual query.