MySqlCommand parameters do not work

Question

In the following code, which is used to get a list of products on a specific line, the command returns results only when I hard-code (concatenate) productLinein SQL. Parameter substitution never occurs.

            + "lineName = '@productLine' "                       
            + "and isVisible = 1 ";
        MySqlDataAdapter adap = new MySqlDataAdapter(sql, msc);
        adap.SelectCommand.Parameters.Add("@productLine", productLine);

Answer 1

        + "lineName = ?productLine "                       
        + "and isVisible = 1 ";
    MySqlDataAdapter adap = new MySqlDataAdapter(sql, msc);
    adap.SelectCommand.Parameters.Add("?productLine", productLine);

• Remove the apostrophes (').
• Change @ to ?, which is the prefix of the parameters in MySql queries.

Answer 2

Delete apostrophes (spelling?). The parameter is around the parameter. They should not be needed.

Answer 3

+ "lineName = '@productLine' " 

+ "lineName = @productLine " 

Answer 4

Is it right that you have

• "lineName = '@productLine'"

to try

• "lineName = @productLine" instead, since @productLine will already be declared as a string type, quotation marks will be added secretly. However, you are actually passing the @productLine string, not the value of the variable.