不接受Java JDBC查询

Question

Hey I'm making a little webapp and have a java file in it with a function what connects a db and fetches the data. But I'm getting a exception anyone knows why because my query is valid if I'm right.

I use eclipse and mysql workbench.

Function:

import java.sql.*;

public class Functions {
    public void dbConn(String nVal, String inpVal){

        System.out.println("Running function...");

        if(nVal != null || inpVal != null){
            String sqlSerch;
            if(nVal.equals("name")){
                sqlSerch = "ID, aNaam FROM profiles WHERE naam = 'casper'";
            }else{
                sqlSerch = "naam, aNaam FROM profiles WHERE ID = " + inpVal;
            }

            //driver / db path
                final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
                final String DB_URL = "jdbc:mysql://localhost:3306/profile";
                //DB user&password
                final String USER = "root";
                final String PASS = "";
                //declare con & sql var
                Connection conn = null;
                Statement stmt = null;
                //register jdbc driver
                try{
                    Class.forName(JDBC_DRIVER);
                    //make a connection
                    conn = DriverManager.getConnection(DB_URL,USER,PASS);
                    //SQL Statement
                    stmt = conn.createStatement();
                    String sql = "SELECT "+ sqlSerch;
                    ResultSet rs = stmt.executeQuery(sql);

                    //Declareer variablen met data uit db
                    //int id = rs.getInt("ID");
                    String naam = rs.getString("naam");
                    String aNaam = rs.getString("aNaam");

                    System.out.println( naam + aNaam);


                    rs.close();
                    stmt.close();
                    conn.close();

                }catch(Exception e){
                    System.out.println(e);
                }


                System.out.println(" - " + nVal + " - " + inpVal);


        }
    }
}

exception:

java.sql.SQLException: Column 'naam' not found.

database structure:

Thank you in advance,

Casper

Answer 1

When you receive "name" through the nVal parameter, you select only ID and aNaam columns.

So, if you try to get values for naam from that ResultSet you get the Exception .

Also, I suggest limiting the results of your query to 1, since you use the WHERE clause with naam and ID , which seem to be not unique, unless there's some constraint not included in the screenshot.

Hope this helped.

Answer 2

You branch and create your queries:

        if(nVal.equals("name")){
            sqlSerch = "ID, aNaam FROM profiles WHERE naam = 'casper'";
        }else{
            sqlSerch = "naam, aNaam FROM profiles WHERE ID = " + inpVal;
        }

Then regardless of the branch, you get your result set values:

        String naam = rs.getString("naam");
        String aNaam = rs.getString("aNaam");

But "naam" will not be in your "ID, aNaam" search.

In general, a good rule of thumb is to always return the same columns.