Select request via c#, what's the problem?

Question

SQL

string Query;
            try
            {              
                if (!string.IsNullOrEmpty(txtSelectByDate1.Text) && !string.IsNullOrEmpty(txtSelectByDate2.Text))                
                     Query = "Select * from Purchase where P_Date >= '"+Convert.ToDateTime(txtSelectByDate1.Text).ToString("yyyy-MM-dd") + 
                     "' and P_Date <= '" + Convert.ToDateTime(txtSelectByDate2.Text).ToString("yyyy-MM-dd") + "'";
                SqlCommand cmd = new SqlCommand(Query, cn);
                SqlDataAdapter sda = new SqlDataAdapter(cmd);
                DataTable dt = new DataTable();
                sda.Fill(dt);
                gvPurchase.DataSourceID = null;
                gvPurchase.DataSource = dt;
            }

In this line, Query gets an error with the description "Use of unassigned local variable 'Query'"
SqlCommand cmd = new SqlCommand(Query, cn);
If you remove this check, then everything works fine.

if (!string.IsNullOrEmpty(txtSelectByDate1.Text) && !string.IsNullOrEmpty(txtSelectByDate2.Text))

Why does it come out like this? Or what way of checking two text boxes for the presence of information would be suitable in this case?

Answer 1

So why are you running a query if you don't initialize query?

var dateFromString = txtSelectByDate1.Text;
var dateToString = txtSelectByDate2.Text;

if (!string.IsNullOrEmpty(dateFromString) && !string.IsNullOrEmpty(dateToString))                
{
    var dateFrom = Convert.ToDateTime(dateFromString).ToString("yyyy-MM-dd");
    var dateTo = Convert.ToDateTime(dateToString).ToString("yyyy-MM-dd");
    
    var query = string.Format("Select * from Purchase where P_Date >= '{0}' and P_Date <= '{1}'", dateFrom, dateTo);
    
    var command = new SqlCommand(query, cn);
    var adapter = new SqlDataAdapter(command);
    var table = new DataTable();
    adapter.Fill(table);
    
    gvPurchase.DataSourceID = null;
    gvPurchase.DataSource = table;
}