Visual C# SQL Database Select Query into Variables

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Hey guys,
I am building a query that will select data from the database based on the value 'RentDue'. I am trying to get the corresponding value 'id'. Given my code below, how will this be possible?

C#

string sql = "SELECT  (ID, RentDue) from Rooms " + "where RentDue = '" + 22 + "')";
                SqlCommand execsql = new SqlCommand(sql, cn);
                cn.Open();

Also, how can I handle multiple results? Once I have obtained the ID, I will appending it to a RichTextView, and I expect there will be more than one result every time the query runs.

Thank you!

Posted 23-Nov-14 15:04pm

Member 10490060

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PIEBALDconsult · Answer 1 · 2014-11-23T15:21:00

Solution 1

0) Don't use string concatenation to for an SQL statement; use a parameterized query.
1) If you are selecting a single value you can use ExecuteScalar
2) If you are selecting multiple values, then you will need something else -- perhaps ExecuteReader.

C#

string sql = "SELECT ID from Rooms where RentDue = @rentdue";
SqlCommand execsql = new SqlCommand(sql, cn);
execsql.Parameters.AddWithValue ( "@rentdue" , 22 ) ;
cn.Open();

... // What do you want to do with it?

Posted 23-Nov-14 15:21pm

PIEBALDconsult

Comments

Member 10490060 23-Nov-14 22:26pm

Thank you very very much! Using ExecuteScalar I have managed to get the first value from the database. However, when there are two values returned by the query, it will only get one of them. This is what I am doing:

execsql.ExecuteNonQuery();

string result = "";
result = Convert.ToString(execsql.ExecuteScalar());

richTextBox1.AppendText(Environment.NewLine);
richTextBox1.AppendText(result);

How can I change this to get all the results, and display them in the richTextBox? Thank you!

PIEBALDconsult 23-Nov-14 22:30pm

ExecuteScalar will get only one result, ExecuteNonQuery will return only a count of how many rows were affected. You may want ExecuteReader.

Don't use Convert.