Check if field in DB is empty, if it is insert ?!?

[jeata]

Hello

I'm again working with databases. Now I have this little problem. I need to insert some data into the database, but before I do that, I must check if the field that I'm inserting data into, already contains some values. If it does, don't insert the data, if it does, insert the data. It takes two integers "winnerid" and "taskid".

Here are the classes
1. Mapper

public boolean setWinner(int winnerid, int taskid, Connection con)
	{
		int rowsInserted = 0;
		 String SQLString = "select * from taskauction where taskid=? and winnerid is null";   
		 
		 String SQLString2 = "update taskauction set winnerid=?"+
	    	                  "where taskid=?";
	      
	     
	       PreparedStatement statement=null;
	       
	       try
	        {
	            //===check if user assigned
	            statement = con.prepareStatement(SQLString);
	            statement.setInt(1,taskid);
	            ResultSet rs  = statement.executeQuery();
	            if (rs.wasNull())
	            {
	            	try{
	      	          statement = con.prepareStatement(SQLString2);
	      	          statement.setInt 	  (1, winnerid);
	      	          statement.setInt    (2, taskid);
	      	             rowsInserted  = statement.executeUpdate();
	      	      }
	      	      catch (Exception e)
	      	      {   
	      	          System.out.println("Fail in TaskAuctionMapper - setWinner");
	      	          System.out.println(e.getMessage());
	      	      }
	      	 
	      	      return rowsInserted == 1;
	             
	            }  
	            else
	            	return rowsInserted == 0;
	        }
	        catch (Exception e)
	        {   
	            System.out.println("Fail");
	            System.out.println(e.getMessage());
	        }
		return rowsInserted == 1;
	       
	      
	    }

2. Controller

public void setWinner(int wid, int tid, Connection con)
    {
        TaskAuctionMapper tam = new TaskAuctionMapper();
       tam.setWinner(wid, tid, con);

    }

3.Button in GUI

private JButton getSelect() {
		if (Select == null) {
			Select = new JButton();
			Select.setBounds(new Rectangle(504, 116, 76, 22));
			Select.setText("Select");
			Select.addActionListener(new java.awt.event.ActionListener() {
				public void actionPerformed(java.awt.event.ActionEvent e) {
					//GET VALUES
					String us = jTextField.getText();
					int userid = Integer.parseInt(us);
					String tis = jTextField1.getText();
					int tid = Integer.parseInt(tis);
					//UPDATE
					try{
						GUIController toc3 = new GUIController();
						toc3.setWinner(userid, tid, cons.getConnection());
                                                annouceField.setText("User assigned !!!");
					}catch (Exception esd)
					{
						System.out.println(esd);
					}
					
					
				}
			});
		}
		return Select;
	}

[d3n1s]

SQL has an if not exist statement you should be able to just plug that in to your insert statement somehow. That's how i do it. or just return a resultset from a test select statement and verify the number of elements in it. If it's 0 then it doesn't exist

[Tolls]

Are you talking about a single field in an existing row, rather than inserting a new row?
If so (and it looks like you are) then a single statement:
UPDATE taskauction SET winnerid=? WHERE taskid=? AND winnerid = NULL

You don't want to select and then update based on the select as the rows may have been updated inbetween the two statements.