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How do I turn my INT (id) into a String in my return from MySQL?

I'm trying to my a very simple webapplication, webshop, for cupcakes.
From the webApp you can choose a cupcake form the dropdown with three attributes
(top, bottom, quantity). These are stored in an ArrayList on my sessionScope but all in numbers e.g. Chokolate as 1 and Vanilla as 2. I want to use these topId numbers to ask my DB (MySQL) for what is in 1 and then have it return Chokolate.
I think I am almost there with my code, but can't get it to return my String, as my topId is an Int.
public static Top getTopById(int topId) {
readFromArrayPutInSQL();
String sql = "INSERT INTO cupcaketopping (toppingType, toppingPrice) VALUES (?, ?)";
try {
ConnectionPool connectionPool = new ConnectionPool();
String query = "SELECT toppingType FROM cupcaketopping";
Statement statement = connectionPool.getConnection().createStatement();
ResultSet rs = statement.executeQuery(query);
rs.getString(topId);
} catch (SQLException e) {
throw new RuntimeException(e);
}
return topId; //Here is the problem - I GUESS?
}
Code after changes due to input in comments, seem to be working!
public static Top getTopById(int topId) {
readFromArrayPutInSQL();
String query = "SELECT toppingType FROM cupcaketopping WHERE toppingID = "+topId+"";
try {
ConnectionPool connectionPool = new ConnectionPool();
PreparedStatement preparedStatement = connectionPool.getConnection().prepareStatement(query);
ResultSet rs = preparedStatement.executeQuery(query);
rs.next();
return new Top(rs.getString(1));
//connectionPool.close(); //NOTE! Won't run, IntelliJ is asking me to delete!
} catch (SQLException e) {
throw new RuntimeException(e);
}
}

There are a few problems:
You're selecting all rows from the cupcaketopping table, regardless of the topId. You should probably be using a PreparedStatement, and then use topId as part of your query.
You never call ResultSet#next(). The result set always starts "before" the first row. You have to call next() for each row in the result set (it returns true if there is a row to read).
The ResultSet#getString(int) method gets the String value of the column at the given index of the result. You only select one column, so the argument should probably be 1 (not topId).
You never close the Statement when done with it.
Depending on how your connection pool class works, you might actually need to close the Connection instead.
You never try to use the String returned by rs.getString(topId).
You never try to convert the query result to a Top instance.
Given it's possible the query will return no result, you might want to consider making the return type Optional<Top>.
The sql string seems to have no purpose.
Your code should look more like this:
public Optional<Top> getTopById(int topId) {
Connection conn = ...;
String query = "SELECT toppingType FROM cupcaketopping WHERE id = ?";
// closes the statement via try-with-resources
try (PreparedStatement stat = conn.prepareStatement(query)) {
stat.setInt(1, topId);
ResultSet rs = stat.executeQuery();
// assume unique result (as it's assumed the ID is the primary key)
if (rs.next()) {
// assumes 'Top' has a constructor that takes a 'String'
return Optional.of(new Top(rs.getString(1)));
} else {
return Optional.empty();
}
} catch (SQLException ex) {
throw new RuntimeException(ex);
}
}
Your actual implementation may vary, depending on how the rest of your code is designed.

Parametrized queries in java

I am facing a problem with retrieving a column from database
This is my code
public String ShowtimeQur(int MovieID)
{
rs3 = null;
String RoomID=null;
String ShowTime = null;
try
{
String qu ="Select Room_ID from Movie_Shows_in where Movie_ID="+MovieID;
//getRoomQur.setInt(1, MovieID);
rs3=getRoomQur.executeQuery(qu);
RoomID=rs3.getString("Room_ID");
getShowtimequr.setString(1, RoomID);
rs4=getShowtimequr.executeQuery();
ShowTime=rs4.getString("Show_Times");
}
catch (SQLException e)
{
e.printStackTrace();
}
return ShowTime;
}
I keep get this type of error
java.sql.SQLException: Invalid operation at current cursor position.

Use PreparedStatement.
PreparedStatement statement = con.prepareStatement("Select Room_ID from Movie_Shows_in where Movie_ID=?");
statement.setInt(1, MovieID);
ResultSet res = statement.executeQuery()
...
rest of your code
Never, never, never use string concatenation to build queries, as you put yourself at risk of SQL Injection

Like the answer before, you shoud declare a "ResulSet result" variable, and after the execute of the query, you should call "result.next()" method to point the cursor on the first row (initially is pointed to row 0 which does not exist) and then call a retrive data mehod like "result.getString(columnNumber)" by example.

Query executed twice (by error) in Java with unwanted values

I'm using JFreeChart to create a chart in Java and MySQL.
When I try to insert my values in another table the query seems to be executed twice since I end up with the same timestamps multiple times...
Here's a part of my code :
private JDBCXYDataset createDataset() {
try {
Connection conn = DriverManager.getConnection(
"jdbc:mysql://localhost:bd?serverTimezone=UTC","MySQL", "MySQL");
conn.setAutoCommit(false);
SQLException savedException = null;
Statement st = conn.createStatement();
st.execute("DROP TABLE IF EXISTS test ");
st.execute("create table test(Table timestamp, Table float,Table float)");
String Date_Debut = "2020-06-25 00:00:00";
String Date_Fin = "2020-06-26 00:00:00";
String sql1 = "INSERT INTO test (Table ,Table ,Table ) "
+ "SELECT Table ,Table ,Table "
+ "FROM Table "
+ "WHERE Table BETWEEN ? AND ? ";
try ( PreparedStatement ps = conn.prepareStatement(sql1)){
ps.setString(1,Date_Debut);
ps.setString(2, Date_Fin);
ps.executeUpdate();
ps.close();
JDBCXYDataset jds = new JDBCXYDataset(conn);
st.close();
jds.executeQuery("SELECT Table ,Table ,Table FROM test");
conn.commit();
return jds;
} catch (SQLException ex) {
savedException = ex;
conn.rollback();
} finally {
conn.setAutoCommit(true);
if(savedException != null) {
throw savedException;
}
}
} catch (SQLException ex1) {
}
return null;
}
EDIT : Actually it seems like the errors where comming directly from the database, the moderators can delete this post if they want. However I keep Trashgod's response validated as it was more than helpful.
For everyone that might come here with a similar issue, inspect in detail your database first to see if it isn't comming from there instead of your code.

Chasing down anomalies in data is arduous, but JFreeChart can at least make the result easier to visualize. Some heuristics for testing:
To verify that the the presumed duplicates in your tabular listing are indeed duplicates, format the timestamps to include milliseconds, e.g. add an S to a SimpleDateFormat or A to a DateTimeFormatter.
For study, temporarily pass the query directly to JDBCXYDataset, and add an ORDER BY clause (untested):
jds.executeQuery(
"SELECT Date_Heure, PV, SV FROM cmd3 "
+ "WHERE Date_Heure BETWEEN "
+ "2020-06-25 00:00:00 AND 2020-06-26 00:00:00 "
+ "ORDER BY Date_Heure");
Enable tooltips in your ChartFactory, as you did here, to see data values in situ. This may suggest additional conditions for your WHERE clause, e.g. PV BETWEEN 5.1 AND 5.9.
Use the interactive JFreeChart pan/zoom controls, discussed here to examine the data; add suitable buttons, shown here, if it will make it easier for colleagues to see your findings.
By design, JDBCXYDataset executes a query defined by a String. If your design needs to display data from a query defined by a PreparedStatement, you can use the existing implementation as a guide.
public class PreparedDataset extends AbstractXYDataset
implements XYDataset, TableXYDataset, RangeInfo {
private final PreparedStatement ps;
public PreparedDataset(PreparedStatement ps) {
this.ps = ps;
}
…
}

SQLite Query With Parameters Not Working in Java

I have a program that selects from a database given a table and column string.
public void selectAllFrom(String table, String column){
String sql = "SELECT ? FROM ?";
try (Connection conn = this.connect();
PreparedStatement pstmt = conn.prepareStatement(sql)){
pstmt.setString(1, column);
pstmt.setString(2, table);
ResultSet rs = pstmt.executeQuery();
while (rs.next()){
System.out.println(rs.getString(column));
}
} catch (SQLException e){
System.out.println(" select didn't work");
System.out.println(e.getMessage());
}
}
For some reason it is not working and it is going right to catch
Here is the connect() function as well:
private Connection connect(){
Connection conn = null;
// SQLite connection string
String url = "jdbc:sqlite:C:/sqlite/db/chinook.db";
try{
// creates connection to the database
conn = DriverManager.getConnection(url);
System.out.println("Connection to SQLite has been established");
} catch (SQLException e){
System.out.println(e.getMessage());
System.out.println("Connection didn't work");
}
return conn;
}
I know the problem is not with the database because I'm able to run other select queries without parameters. It is the parameters that are giving me the problem. Can anyone tell what the problem is?

A table or column name can't be used as a parameter to PreparedStatement. It must be hard coded.
String sql = "SELECT " + column + " FROM " + table;
You should reconsider the design so as to make these two constant and parameterize the column values.

? is a place holder to indicate a bind variable. When a SQL statement is executed, database first checks syntax, and validates the objects being referenced, columns and access permission for specified objects (i.e metadata about objects) and confirms that all are in place and valid. This stage is called parsing.
Post parsing, it substitutes bind variables to query and then proceeds for actual fetch of results.
Bind variables can be substituted in any place in query to replace an actual hard coded data/strings, but not the query constructs them selves. It means
You can not use bind variables for keywords of sql query (ex: SELECT, UPDATE etc.)
You can not use bind variables for objects or their attributes (i.e table names, column names, functions, procedures etc.)
You can use them only in place of a otherwise hard coded data.
ex: SELECT FIRST_NAME, LAST_NAME, 'N' IS_DELETED FROM USER_DATA WHERE COUNTRY ='CANADA' AND VERIFIED_USER='YES'
In above sample query, 'N','CANADA' and 'YES' are the only strings which can be replaced by a bind variable, not any other word.
Using bind variable is best practice of coding. It improves query performance (when used with large no. of queries in tuned database products like Oracle or MSSQL) and also protects your code against sql injection attacks.
Constructing query by concatenating strings (especially data part of query) is never recommended way. You can still construct a query by concatenation for other parts like table name or column name as long as those strings are not directly taken from input.
Below example is acceptable:
query = "Select transaction_id, transaction_date from ";
if (isHistorical(reportType)
{ query = query + "HISTORY_TRANSACTIONS" ;}
else
{query = query + "PRESENT_TRANSACTIONS" ; }
recommended practice is to use
String query_present = "SELECT transaction_id, transaction_date from PRESENT_TRANSACTIONS";
String query_historical = "SELECT transaction_id, transaction_date from HISTORY_TRANSACTIONS";
if (isHisotrical(reportType))
{
ps.executeQuery(query_historical);
}else{
ps.executeQuery(query_present);
}

Unable to get value from ResultSet

I am working on a web application using Java and MySQL.
I created a method that is supposed to return an ArrayList of the respective column name based on the various tables in the database.
However, when I debugged the method, I realised the while(rs.next()) causes an error. I used this site for reference, hence I am not sure what went wrong.
This is the code. Thanks.
// Returns the the all the columns in the table
public ArrayList getColumnName(String tableName) throws SQLException {
ResultSet rs = null;
List<String> columnName = new ArrayList<String>();
Statement st = null;
Connection con = null;
try {
// Get a connection from the connection factory
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/information_schema", "root", "xxxx");
// Create a Statement object so we can submit SQL statements to the driver
st = con.createStatement();
StringBuilder sql = new StringBuilder("SELECT column_name FROM information_schema.columns " +
"WHERE table_schema = 'testDB' AND table_name = '");
sql.append(tableName).append("'");
rs = st.executeQuery(sql.toString());
while (rs.next()) { // getting error..
columnName.add(rs.getString("column_name"));
}
} catch (SQLException ex) {
Logger.getLogger(ModificationPage.class.getName()).log(Level.SEVERE, null, ex);
} finally {
if (con != null || st != null) {
st.close();
con.close();
}
}
return (ArrayList) columnName;
}

According to the Javadoc of 1.6 (not sure which version of Java you're using):
Throws:
SQLException - if a database access error occurs or this method is called on a closed result set
It's very, very unlikely that if you actually got to the line where rs.next() was called, that a database error occurred just then. So, the most likely result is that the result set was closed.
Please alter your code to the following and see if you still get the error on the same line:
while (!rs.isClosed() && rs.next()) { // getting error..
columnName.add(rs.getString("column_name"));
}
Also, Holy SQL Injection Attack, Batman!
Taking the raw string as you're doing and enclosing it within single quotes leads this code to have an SQL injection vulnerability. Basically all a malicious user has to do is end your query with a single quote (') and run a query of their own afterwards.

So, the exception never happens ?
A query error should be thrown at rs = st.executeQuery(sql.toString()) if that were the case, but if it make it to whileand didn't iterate, it's because of an empty resultset
Maybe you're passing wrong arguments to the query ?