SQL C＃，命令（查询）执行两次

Question

I have simple app to build sql query (for educational purposes). I created textarea where user can write his command to sql, then program has to execute it or catch Sqlexeption. I know about safety etc. but its ok- user can delete everything :)

ok. here is the code:

query = text from textarea(its SQL command)

if (!String.IsNullOrEmpty(query) || !String.IsNullOrWhiteSpace(query))
{
    string conString = ConfigurationManager.ConnectionStrings["StudentDataBase"].ConnectionString;

    try
    { 
        using (SqlConnection SqlCon = new SqlConnection(conString))
        {                
            try
            {
                SqlCommand command = new SqlCommand(query, SqlCon);
                SqlCon.Open();

                command.ExecuteScalar();

                int numOfRows = 0;

                SqlDataAdapter adpt = new SqlDataAdapter(command);
                DataTable dt = new DataTable();
                DataSet dset = new DataSet();
                adpt.Fill(dset);
                dt = dset.Tables[0];
                if (dt.Rows.Count > 0)
                {
                    numOfRows = dt.Rows.Count;
                    gridview_results.DataSource = dt;
                    gridview_results.DataBind();

                    Sql_error = "Done. Results: " + numOfRows + " rows.";
                    container_sql_error.Style.Add("background-color", "#b9ffcb");
                }
                else
                {
                    Sql_error = "0 rows to show.";
                }                           

                SqlCon.Close();
            }
             catch (SqlException ex)
            {
               Sql_error = "Error: " + ex.Message;
               container_sql_error.Style.Add("background-color", "#ff9600");
            }
        }
    }
    catch (SqlException ex)
    {
        Sql_error = "Error... " + ex.Message;
        container_sql_error.Style.Add("background-color", "#ff9600");
    }
}

And now, when im trying:

SELECT * FROM test its OK. GridView showing data.

slleeeccct * from testsste its OK - showing an error.

INSERT INTO test (col1) VALUES ('aaa') its NOT OK- program throws error System.IndexOutOfRangeException: cannot find table 0 BUT command was excecuted properly BUT TWICE.

Now i have a questions: why command is excecuting TWICE(2x same data in DB) and why is there an Error about finding table 0 (is it about GridView maybe- cant fill GV with insert into )?

Answer 1

First of all, you are executing the code twice

-> one time you are using ExecuteScalar and the other you are using the SQLAdapter to fill the dataset with returned results, you can just use it like the below:

1- dataset ds=new dataset();

2- adapter.fill(ds);

3- return ds; 

and that's it :)

Regarding the insert query error, that's normal as well because the insert statement using Execute Scalar will 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.

so when you use Insert statement, you are having an error because either

1- the command wasn't executed successfully and returned an error "Check if databsae has the inserted row you just typed"

2- dataset tables has no data, you can make an IF Statement check before you try to read from it like

"If(ds.tables.count>0) {do something}"