ms access database with java

Question

I am creating a java program, with which I am editing into a Microsoft Access Database. I have a certain case, in which I need to search if a certain record already exists in my table, if it does, I want to update it, and if not, I want to create it from scratch.

I have found this piece of code:

IF EXISTS (SELECT * FROM USERS WHERE USERID=@UID) select 1 else select 

This code gives me an error, saying that a SELECT, UPDATE or DELETE statement was expected.

In a code that I have tried my self, I have done the following:

try{
            s = con.createStatement();
            s.executeQuery("SELECT * FROM table WHERE date='" + today + "'");
            rset = s.getResultSet();    

            if (rset.getString("date") == null){

                s = con.createStatement();     
                s.executeUpdate("INSERT INTO table VALUES ('" + today + "','" + cflow + "','" + vat + "','" + cnn + "')");

            }
        }

        catch (SQLException exp)
        {
            System.err.println(exp);
        }

But with this code, when the record does not exist yet, the user input is not updated inside the database.

Thanks for your time :)

Answer 1

1st: If I can remember right, then is

IF EXISTS (SELECT * FROM USERS WHERE USERID=@UID) select 1 else select 

an incomplete transact sql statement -used by the sql engine from a database system.

2nd:

if (rset.getString("date") == null){}

you should avoid this way, because there is a good chance to get a Nullpointer Exception.

In my eyes a better one is a test the size of resultset for zero or the resultset it self for the value of NULL .

In case the UPDATE statement won't also be executed, check your SELECT statement using the database engine -Ms Access, SQL Server, etc.- directly. The advantage is you can exclude a mistake in your SELECT query.

Answer 2

(rset.getString("date") == null)

should be

(!rset.next())

rset is positioned 'before' the first result that gets returned. next() returns true if there was a 'next' result to get.

Also, what datatype is your 'date' variable? There's no guarantee that a date.toString() will format the date correctly for MS-Access version of SQL.

Rather, prepare a statement

PreparedStatement ps = connetion.prepareStatement("SELECT * from table where date=?");

and set the date like

ps.setDate(1, date);

then issue the query using the prepared statement.

That saves any toString() issues. (I haven't compiled this, it almost certainly won't work as-is, but the idea is there).

Answer 3

What about this?

SELECT IF EXISTS (SELECT * FROM USERS WHERE USERID=@UID) THEN 1 ELSE 0 END

or

SELECT IF(EXISTS (SELECT * FROM USERS WHERE USERID=@UID), 1, 0)

(I'm not sure about the real syntax here.)

Answer 4

Here is what i used to find the last ID in a table. IF the table is empty the no ID will be returned. If table is populated then i needed the next ID for new record.

 ResultSet mn = stmt.executeQuery("SELECT MAX(ExamID)FROM ExamResults"); if (mn == null){ jTextField1.setText("1"); } else{ while (mn.next()) { int lastID =Integer.parseInt(""+(mn.getObject(1))); jTextField1.setText(""+(lastID+1)); } } // close the objects mn.close(); stmt.close(); conn.close();