how checkBox populates the listBox?

Question

I have a database, which has atable called Company. Inside are columns with the basic informations (company name, street, post, city, tel.numbers, ...). I would like to know to populate listBox with company names which have a "stationary number" in the database when checkBox is checked! But I mean if the column "StationaryNumber" is NULL, then this comany shouldn`t be included in the listBox, if the company has a number (column is NOT NULL) then the name of the is company MUST be incuded in the listBox! I have this example for a textBox: cmd.Parameters.Add(new SqlParameter("@stationary", System.Data.SqlDbType.VarChar, 40, "Stationary")); cmd.Parameters["@stationary"].Value = textBox.Text; ..let` say if I write in the textBox a telephone number which is in the StationaryNumber column, it will populate the listBox with the companies which have this number(it should be just one company). But, if I want to put a checkBox like: cmd.Parameters.Add(new SqlParameter("@stationary", System.Data.SqlDbType.VarChar, 40, "Stationary")); cmd.Parameters["@stationary"].Value = ??; //OR this whole row is wrong - it has to be bind to the "Stationary" Column somehow. ... How to code these 2 last lines that the readed will read from a database (column "StationaryNumber") ... What has to be instead of ??? to get into my listBox all the company names, which have the telephone number in Stationary column For a better idea what I am doing, take a look at THIS picture. In the buttom right you will notice checkBoxes. This is what I wanna do. There is example of choosing just number which starts with 080, or 090 or stationary number ,...