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Why does this Query return NULL?

I have a derby users database which I query, when the user clicks login on the application.
However, when I query the users table with the parameter [user] derby returns a null Object instead of the record it ought to return.
Here is my code:
String ssql = "SELECT * FROM USERS WHERE UNAME LIKE ?";
try{
DriverManager.registerDriver(new org.apache.derby.jdbc.EmbeddedDriver());
con = DriverManager.getConnection(url);
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
try{
while (rs.next()) {
if(rs.getString("PW").toCharArray().equals(txt_password.getPassword())){
sql.close();
con.close();
return true;
}
} catch (NPE ...) {...}
}
I tried it multiple times wit a test user with both the pw and the username set to "test"; but I always get the same error.
Why is the recordset always Null?
Thanks for your help :)

The documentation says
ResultSet getGeneratedKeys() throws SQLException
Retrieves any auto-generated keys created as a result of executing this Statement
object.
If this Statement object did not generate any keys, an empty
ResultSet object is returned.
Your select statement isn't generating any keys that's why it's returning an empty ResultSet. You aren't inserting anything hence no keys are being generated.
You can try ResultSet rs = sql.executeQuery();. It should work.

You are using it in wrong way.
The generated keys concept should be used only in the case DML of insert type query but not in the case of select query.
select simply select the rows from the table. In this case there is no chance of any keys getting generated.
In the case of insert query if any column is configured as auto increment or kind of functionality then some keys will get generated. These keys can be caught using Statement.RETURN_GENERATED_KEYS in java.
As you are using select query there is no need of using Statement.RETURN_GENERATED_KEYS.
You just modify below lines and everything will be fine.
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
with
sql = con.prepareStatement( ssql );
sql.setString( 1, cbox_chooseUser.getSelectedItem().toString() );
ResultSet rs = sql.executeQuery();

SQLException deleting row from JTable and database

I want to delete selcetd row in a JTable from both the table itself and the database.
That is my code:
Object number = jTable1.getValueAt(selectedRow-1, 0);
String sql = "delete from orders where number ="+number;
Statement st = conn.createStatement();
rs = null;
rs = st.executeQuery(sql);
When the excuteQuery() runs I get the following exception:
(java.sql.SQLException) java.sql.SQLException: Can not issue data manipulation statements with executeQuery()
What am I doing wrong?

It is not an Abnormal Exception.
You need to call executeUpdate instead of executeQuery. You cannot update database by calling executeQuery method. To update something in database (insert, update, delete) you need to call executeUpdate method and it will not return the ResultSet and instead return you an int value.
int result = st.executeUpdate(sql);
More Info

Java PreparedStatement Delete Query: Show Number of Rows Deleted?

I have a PreparedStatement with a MySQL query that deletes rows based on a timestamp criteria. Is it possible to pull out how many rows were deleted from that same delete prepared statement or would I have to run a separate query to get the number first? This is what I tried but it didn't work:
PreparedStatement pstmt = conn.prepareStatement(delete, PreparedStatement.RETURN_GENERATED_KEYS);
pstmt.setString(1, keyword);
pstmt.executeUpdate();
ResultSet rs = pstmt.getGeneratedKeys();
while (rs.next())
{
n = rs.getInt(1);
}
rs.close();
pstmt.close();
conn.close();
Sorry guys, I figured it out. int n = pstmt.executeUpdate();

One way to do it would be trusting in the result of PreparedStatement#executeUpdate:
Returns either (1) the row count for SQL Data Manipulation Language (DML) statements or (2) 0 for SQL statements that return nothing
Another way could be using a SELECT COUNT(*) statement before executing the delete statement. Note that you can do both in a single connection/transaction in order to not affect the results.

Getting a result back from a stored procedure in Java

I am having the hardest time calling an Oracle stored procedure from a java runtime environment. The stored procedure that I am calling has 2 parameters 1 in and 1 out. Here is how I call the stored procedure... How do you get the resultSet from an Oracle ref_cursor
ds = (DataSource)initialContext.lookup("JDBC/EPCD13DB");
conn = ds.getConnection();
callableStatement = conn.prepareCall(storedProcCall);
callableStatement.setString(1, input1);
callableStatement.registerOutParameter(2, OracleTypes.CURSOR);
callableStatement.execute();//(ResultSet) callableStatement.getObject(1);
ResultSet rs = callableStatement.getResultSet();
while(rs.next()){
Provider tempProv = new Provider();
tempProv.setResourceId(rs.getLong("res_id"));
tempProv.setFirstName(rs.getString("First_Name"));
tempProv.setLastName(rs.getString("Last_Name"));
tempProv.setMiddleName(rs.getString("Middle_Name"));
ObjList.add(tempProv);
}
rs.close();

You should be able to retrieve the ResultSet with:
ResultSet rSet = (ResultSet)callableStatement.getObject(2);

Does this help you? Seems like you have to call getObject and cast it into a result set before querying on the result set.
Credit:: http://www.mkyong.com/jdbc/jdbc-callablestatement-stored-procedure-cursor-example/

I believe it returns only one output(oracle cursor)
ResultSet rs=(ResultSet) callableStatement.getObject(2);
and then iterate your cursor result set for records inside:
while(rs.next()){
Provider tempProv = new Provider();
tempProv.setResourceId(rs.getLong("res_id"));
tempProv.setFirstName(rs.getString("First_Name"));
tempProv.setLastName(rs.getString("Last_Name"));
tempProv.setMiddleName(rs.getString("Middle_Name"));
ObjList.add(tempProv);
}

In spring framework fetching database cursor results can be easily achieved. It has inbuilt classes like maprow, storedprocedure to serve the purpose. PFB the link
http://static.springsource.org/spring/docs/3.1.x/spring-framework-reference/html/jdbc.html#jdbc-simple-jdbc-call-1

Get last insert id with Oracle 11g using JDBC

I'm new to using Oracle so I'm going off what has already been previously answered in this SO question. I just can't seem to get it to work. Here's the statement that I'm using:
declare
lastId number;
begin
INSERT INTO "DB_OWNER"."FOO"
(ID, DEPARTMENT, BUSINESS)
VALUES (FOO_ID_SEQ.NEXTVAL, 'Database Management', 'Oracle')
RETURNING ID INTO lastId;
end;
When I call executeQuery the PreparedStatement that I have made, it inserts everything into the database just fine. However, I cannot seem to figure out how to retrieve the ID. The returned ResultSet object will not work for me. Calling
if(resultSet.next()) ...
yields a nasty SQLException that reads:
Cannot perform fetch on a PLSQL statement: next
How do I get that lastId? Obviously I'm doing it wrong.

make it a function that returns it to you (instead of a procedure). Or, have a procedure with an OUT parameter.

Not sure if this will work, since I've purged all of my computers of anything Oracle, but...
Change your declare to:
declare
lastId OUT number;
Switch your statement from a PreparedStatement to a CallableStatement by using prepareCall() on your connection. Then register the output parameter before your call, and read it after the update:
cstmt.registerOutParameter(1, java.sql.Types.NUMERIC);
cstmt.executeUpdate();
int x = cstmt.getInt(1);

I tried with Oracle driver v11.2.0.3.0 (since there are some bugs in 10.x and 11.1.x, see other blog). Following code works fine:
final String sql = "insert into TABLE(SOME_COL, OTHER_COL) values (?, ?)";
PreparedStatement ps = con.prepareStatement(sql, new String[] {"ID"});
ps.setLong(1, 264);
ps.setLong(2, 1);
int executeUpdate = ps.executeUpdate();
ResultSet rs = ps.getGeneratedKeys();
if (rs.next() ) {
// The generated id
long id = rs.getLong(1);
System.out.println("executeUpdate: " + executeUpdate + ", id: " + id);
}

When you prepare the statement set the second parameter to RETURN_GENERATED_KEYS. Then you should be able to get a ResultSet off the statement object.

You can use Statement.getGeneratedKeys() to do this. You just need to make sure to tell JDBC what columns you want back using one of the method overloads for that, such as the Connection.prepareStatement overload here:
Connection conn = ...
PreparedStatement pS = conn.prepareStatement(sql, new String[]{"id"});
pS.executeUpdate();
ResultSet rS = pS.getGeneratedKeys();
if (rS.next()) {
long id = rS.getLong("id");
...
}
You don't need to do the RETURNING x INTO stuff with this, just use the basic SQL statement you want.

Are you doing that in a stored procedure ? According to this Oracle document, it won't work with the server-side driver.
The Oracle server-side internal driver does not support
the retrieval of auto-generated keys feature.