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Java: SQL Query: rs.next() is false after updating a column

I have a strange problem. I have a database and I want to change the values of a column. The values are safed in an Arraylist (timelist).
In order to write the values in the right row, I have a second Arrylist (namelist). So I want to read the first row in my Database, than I check the namelist and find the name. Than i take the matching value out of the timelist and write it into the database into the column "follows_date" in the row, matching to the name.
And than I read the next row of the Database, until there are no more entries.
So the strange thing is, if I change nothing in the database, the while(rs.next()) part works.
For example:
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //liest die namen
}
}
This would print me every name after name. But when I change the table, the while loop ends after that. (no error, the program just finishes)
ResultSet rs = statement.executeQuery("SELECT username FROM users");
while(rs.next()){
// read the result set
String name = rs.getString("username");
System.out.println("username = " + name); //writes the name
//look, if name is in Arraylist "namelist"). if yes, than write the matching date from "timelist" into the database.
if (namelist.contains(name)){
System.out.println("name found: "+ name);
int listIndizi = namelist.indexOf(name); //get index
Long indiziDatum = (long) timelist.get(listIndizi); //get date from same Index
System.out.println(indiziDatum); // print date so i can see it is correct (which it is)
statement.executeUpdate("UPDATE users SET follows_date ="+ indiziDatum +" WHERE username = '"+name+"'"); //updates the follows_date column
}
}
Everything works fine, except that now, the while loop doesn't continues after the first passage, but ends.

The resultSet of a statement is closed and will not return further results if you execute another statement. Create a new separate statement object for the update and everything should work as excepted.
Statement statement1 = connection.createStatement();
Statement statement2 = connection.createStatement();
ResultSet resultSet1 = statement1.executeQuery("SELECT username FROM users");
while(resultSet1.next()){
...
statement2.executeUpdate("UPDATE users ..."));
}

As to Why it happens:
Here is the explanation from the official documentation:
A ResultSet object is automatically closed when the Statement object that generated it is closed, re-executed, or used to retrieve the next result from a sequence of multiple results.
Alternative Approach:
From your sample, it seems you are trying to update the "same" row in your resultSet, you should consider using an Updatable ResultSet.
Sample code from the official documentation:
public void modifyPrices(float percentage) throws SQLException {
Statement stmt = null;
try {
stmt = con.createStatement();
stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = stmt.executeQuery(
"SELECT * FROM " + dbName + ".COFFEES");
while (uprs.next()) {
float f = uprs.getFloat("PRICE");
uprs.updateFloat( "PRICE", f * percentage);
uprs.updateRow();
}
} catch (SQLException e ) {
JDBCTutorialUtilities.printSQLException(e);
} finally {
if (stmt != null) { stmt.close(); }
}
}

Return values from DB with another result set

How can I execute this statement and process it java. Is it possible to get a return value and then the next resultset which is the select to employee in the way I'm doing it?
I cannot find the accurate way on Google to perform what I want because all of the examples are results with single SELECTs and cannot find a query with RETURN from DB. But according to this question, it is possible to manage multiple result sets from DB (java) as .NET can do.
I'm using postgresql 9.4 and I don't want to use a stored proc (function) to do what I'm trying to do.
This is the code that I've been trying to test, but I get an exception that there is a syntax error in 'IF' line 1
public Employee getEmployee(Connection con, String code) {
Employee employee = new Employee();
try {
String query =
"IF EXISTS(SELECT * FROM employee WHERE code = ?) THEN "
+ "RETURN 1; "
+ "ELSE "
+ "RETURN 2; "
+ "END IF; "
+ "SELECT EmployeeID, FirstName FROM employee where code = ?; ";
PreparedStatement stmt = con.prepareStatement(query);
stmt.setString(1, code);
stmt.setString(2, code);
boolean hasResults = stmt.execute();
int returnValue = 0;
while(hasResults){
ResultSet rs = stmt.getResultSet();
returnValue = rs.getInt(1);
if(returnValue == 1){
hasResults = stmt.getMoreResults();
while(hasResults){
employee.setId(rs.getInt("EmployeeID"));
employee.setFirstName(rs.getString("FirstName"));
}
}
}
return employee;
} catch (Exception e) {
System.out.println(e.getMessage());
return null;
}

You are overcomplicating things (apart from the fact that there is no if in SQL).
Just run the select, if there is no such employee you'll get an empty result set:
public Employee getEmployee(Connection con, String code) {
Employee employee = new Employee();
try {
String query = "SELECT EmployeeID, FirstName FROM employee where code = ?";
PreparedStatement stmt = con.prepareStatement(query);
stmt.setString(1, code);
ResultSet rs = stmt.executeQuery();
if (rs.next()){
employee.setId(rs.getInt("EmployeeID"));
employee.setFirstName(rs.getString("FirstName"));
}
return employee;
} catch (Exception e) {
System.out.println(e.getMessage());
return null;
}
}
You also might want to move the creation of the Employee instance inside the if (rs.next()) so that if no employee exists your method returns null. The above code would always return an Employee even if there is none
You also should remove the ; from the query string. Although the Postgres driver will happily run statements terminated with ; this is not JDBC compliant and other drivers (or DBMS) might refuse to run it.

Java- select certain rows from column with SQLite

Sorry if the title is not precise.
I am using a custom class to get data from a SQLite database.
For example:
the method below is supposed to return list of users, which are members of a certain department.
Each user in the USER table has a column with id of the department he belongs to.
At the moment I am getting all the users and then comparing their department IDs to the targetID of the department I am looking for.
Is there a way to get just the set of users that have a particular department ID, so that I don't have to check each one's department id?
private List<User> getDepartmentMembers(int targetID) {
List<User> members = new ArrayList<User>();
Connection c = null;
Statement statement = null;
try {
Class.forName("org.sqlite.JDBC");
c = DriverManager.getConnection("jdbc:sqlite:TheatroData.sqlite");
c.setAutoCommit(false);
statement = c.createStatement();
ResultSet rs = statement.executeQuery( "SELECT * FROM USERS;" );
while ( rs.next() ) {
int id = rs.getInt(Constants.ID_KEY);
if (id == targetID ){
User tmp = null;
int position = rs.getInt(Constants.POSITION_KEY);
if (position == Constants.DEPARTMENT_HEAD)
tmp = new DepartmentHead();
else if (position == Constants.DEPARTMENT_MANAGER)
tmp = new DepartmentManager();
else if (position == Constants.DEPARTMENT_MEMBER);
tmp = new GruntUser();
tmp.setID(id);
tmp.setName(rs.getString(Constants.NAME_KEY));
tmp.setPosition(position);
tmp.setUsername(rs.getString(Constants.USERNAME_KEY));
tmp.setLastname(rs.getString(Constants.SURNAME_KEY));
tmp.setDepartment(targetID);
tmp.setPassword(rs.getString(Constants.PASS_KEY));
members.add(tmp);
}
}
rs.close();
statement.close();
c.close();
} catch ( Exception e ) {
System.err.println( e + " -in getDepartmentMembers" + e.getClass().getName() + ": " + e.getMessage());
}
return members;
}
I was thinking I need something like this:
ResultSet rs = statement.executeQuery( "SELECT * FROM USERS where department = ?;", targetID );

In an ideal world, you could do it as you wrote:
ResultSet rs = statement.executeQuery( "SELECT * FROM USERS WHERE department = ?;", targetID );
But, executeQuery from JDBC does currently not provide the possibility for argument binding. So you have to use "Prepared Statements".
Instead of
statement = c.createStatement();
ResultSet rs = statement.executeQuery( "SELECT * FROM USERS;" );
do:
prepared = c.prepareStatement("SELECT * FROM USERS WHERE department = ?;");
prepared.setString(1, targetID);
ResultSet rs = prepared.executeQuery();
When you need more than one parameter, you can use a different syntax for replacing it, for example "?001". See SQLite Documentation: C/C++ Interface Section 5.
Also remove the Java coding for your own selection of the right department.
Since the CluelessStudent presented a different solution, involving string concatenation, I want to say the following:
I would definitively discourage string concatenation! You always
should use argument binding and not string concatenation! String
concatenation is a huge security risk, since it can be used for so
called "SQL injection attacks". See Wikipedia: SQL Injection

Yes you pratcially answered your own question. You can also do like this.
String query = "SELECT * FROM USERS where department = (?)";
PreparedStatement statement = c.prepareStatement(sql);
statement.setInt(1, targetId);
ResultSet rs = statement.executeQuery();
while(rs.next()){
//you get only records that have id = targetId
}
//close rs, statement and connection!!!

I was just passing a wrong statement. The correct way:
ResultSet rs = statement.executeQuery( "SELECT * FROM USERS where department = "+targetID+";");

SQL command from eclipse using JDBC

I have been searching and trying different stuff for awhile, but have not found an answer. I'm trying to make a connection to sql using JDBC from eclipse. I am having trouble when I need to select a string in the database. If I use:
Select name from data where title = 'mr';
That works with terminal/command line but when I try to use eclipse where I use
statement sp = connection.createstatement();
resultset rs = sp.executequery("select name from data where title = '" + "mr" + "'");
It does not give me anything while the terminal input does. What did I do wrong in the eclipse? Thanks
Heres a part of the code. Sorry, its a bit messy, been trying different things.
private boolean loginChecker(String cid, String password) throws SQLException{
boolean check = false;
PreparedStatement pstatment = null;
Statement stmt = null;
//String query = "SELECT 'cat' FROM customer";
String query = "select '"+cid+"' from customer where password = '"+password+"'";
try {
System.out.println("in try......");
//stmt = con.createStatement();
//ResultSet rs = stmt.executeQuery(query);
PreparedStatement prepStmt = con.prepareStatement(query);
ResultSet rs = prepStmt.executeQuery();
//System.out.print(rs.getString("cid"));
while(rs.next()){
check = true;
System.out.print(rs.getString("cid"));
}
} catch (SQLException e ) {
e.printStackTrace();
} finally {
if (stmt != null) {
//stmt.close();
}
}
return check;
}
Second try on a simpler query:
public List<Object> showTable() {
List<Object> result = new ArrayList<Object>();
String name = "bob";
try
{
PreparedStatement preStatement = con.prepareStatement("select total from test where name = ?");
preStatement.setString(1, name);
ResultSet rs1 = preStatement.executeQuery();
while(rs1.next()){
System.out.println("there");
System.out.println(rs1.getInt("total"));
}
}
catch (SQLException ex)
{
System.out.print("Message: " + ex.getMessage());
}
return result;
}

Remove the quotes around the column name.
String query = "select "+cid+" from customer where password = '"+password+"'";
You've not mentioned which database you're working with but many databases like Oracle change the column case to upper case unless they're quoted. So, you only quote table columns if that's how you had created them. For example, if you had created a table like
CREATE TABLE some_table ( 'DoNotChangeToUpperCase' VARCHAR2 );
Then you would have to select the column with quotes as well
SELECT 'DoNotChangeToUpperCase' FROM some_table
But, if you didn't create the table using quotes you shouldn't be using them with your SELECTs either.

Make sure you are not closing the ResultSet before you are trying to use it. This can happen when you return a ResultSet and try to use it elsewhere. If you want to return the data like this, use CachedRowSet:
CachedRowSet crs = new CachedRowSetImpl();
crs.populate(ResultSet);
CachedRowSet is "special in that it can operate without being connected to its data source, that is, it is a disconnected RowSet object"
Edit: Saw you posted code so I thought I add some thoughts. If that is your ACTUAL code than the reason you are not getting anything is because the query is probably not returning anything.
String query = "select '"+cid+"' from customer where password = '"+password+"'";
This is wrong, for two reasons. 1) If you are using prepared statements you should replace all input with '?' so it should look like the following:
String query = "select name from customer where password = ?";
Then:
PreparedStatement prepStmt = con.prepareStatement(query);
prepStmt.setString(1, password);
ResultSet rs = prepStmt.executeQuery();
2)
System.out.print(rs.getString("cid"));
Here are are trying to get the column named "cid", when it should be the name stored in cid. You should actually never be letting the user decide what columns to get, this should be hardcoded in.

How to get a particular column's values alone?

I am using the mysql java connector. I need java to display the contents of the first column and the second column in different steps. How do I achieve this?
String qry = "select col1,col2 from table1";
Resultset rs = statement.executeQuery(qry);

I've posted a sample below:
Statement s = conn.createStatement ();
s.executeQuery ("SELECT id, name, category FROM animal");
ResultSet rs = s.getResultSet ();
int count = 0;
while (rs.next ())
{
int idVal = rs.getInt ("id");
String nameVal = rs.getString ("name");
String catVal = rs.getString ("category");
System.out.println (
"id = " + idVal
+ ", name = " + nameVal
+ ", category = " + catVal);
++count;
}
rs.close ();
s.close ();
System.out.println (count + " rows were retrieved");
(From: http://www.kitebird.com/articles/jdbc.html#TOC_5 )
Edit: just re-read the question and think you might mean you want to refer to a column later on in code, instead of in the inital loop as in my example above. In that case, you can create an array and refer to the array later on, or, as another answer suggests you can just do another query.

Load them into any data structure of your choice and then display them to your heart's content.
List<String> firstCol = new ArrayList<String>();
List<String> secondCol = new ArrayList<String>();
while(rs.next()){
firstCol.add(rs.getString("col1"));
secondCol.add(rs.getString("col2"));
}
Then you can manipulate with the two list as you want.

How about ... (insert drumroll here):
String qry1 = "select col1 from table1";
Resultset rs1 = statement.executeQuery(qry);
String qry2 = "select col2 from table1";
Resultset rs2 = statement.executeQuery(qry);
(You might want to phrase your question more clearly.)

You can do it like this :
String sql = "select col1,col2 from table1";
ResultSet rs = stmt.executeQuery(sql);
while (rs.next()) System.out.println(rs.getString("col1"));

I am using following Code:
Statement sta;
ResultSet rs;
try {
sta = con.createStatement();
rs = sta.executeQuery("SELECT * FROM TABLENAME");
while(rs.next())
{
Id = rs.getString("COLUMN_Name1");
Vid = rs.getString("COLUMN_Name2");
System.out.println("\n ID : " + Id);
System.out.println("\n VehicleID: " + Vid);
}
}
catch(Execption e)
{
}
And this code is 100% working.

String emailid=request.getParameter("email");
System.out.println(emailid);
rt=st.executeQuery("SELECT imgname FROM selection WHERE email='emailid'");
System.out.println(rt.getString("imgname"));
while(rt.next())
{
System.out.println(rt.getString("imgname"));
finalimage=rt.getString("imgname");
}