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Trouble with SQL query

I'm new in database and sql, and just trying to figure it all out in Java, but I got stuck with some minor problem, I'm trying to remove one record in db, with id that is given as method parameter, like this, but it's not working
#Override
public void removeCustomer(int number) {
Statement statement = null;
try {
statement = connection.createStatement();
statement.executeUpdate("DELETE FROM Customers WHERE id='number'");
} catch (SQLException e) {
e.printStackTrace();
} finally {
try{
if(statement != null) statement.close();
} catch (SQLException e ) {
e.printStackTrace();
}
}
}
It does work, when I write in SQL query " ... WHERE id='2'";
But I want to be able to pass the number from method parameter.
Anyone could help?

You can use PreparedStatement like so :
try(PreparedStatement stm = connection.createStatement("DELETE FROM Customers WHERE id=?")){
stm.setInt(1, number);
stm.executeUpdate();
}
//.. catch and finally
Note
It does work, when I write in SQL query " ... WHERE id='2'";
If in case your id is a varchar you can pass a string to the statement by using setString instead of setInt, but I don't suggest to use string for id

SQL Lite Query (between in dates) doesn't work

in my small test program I have some SQL Queries. The first SELECT * FROM kilometer; works properly and returns all the columns in the table. So in Java embedded, ResultSet rs = stmt.executeQuery("SELECT * FROM kilometer;"); returns an ResultSet which is not empty.
Now I wanted to get only the rows within a specific date. But my embedded query ResultSet rs = stmt.executeQuery("SELECT * FROM kilometer WHERE datum BETWEEN '2016-01-01' AND '2016-12-31';"); returns an empty ResultSet. But I've tested it online and it worked properly. Where is my mistake? I've consulted already some pages like this, but I can't find the mistake.
I am using SQLite 3.15.1 and Java SE 8.
Full java code:
public ArrayList<Strecke> getErgebnisse(final String startzeitpunkt, final String zielzeitpunkt) {
ArrayList<Strecke> strecken = new ArrayList<>();
try {
try {
if (connection != null) {
}
connection = DriverManager.getConnection("jdbc:sqlite:" + DB_PATH);
if (!connection.isClosed())
} catch (SQLException e) {
throw new RuntimeException(e);
}
Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM kilometer WHERE datum BETWEEN '2016-01-01' AND '2016-12-31';");
while (rs.next()) {
strecken.add(new Strecke(Instant.ofEpochMilli(rs.getDate("datum").getTime()).atZone(ZoneId.systemDefault()).toLocalDate(), rs.getString("startort"), rs.getString("zielort"), rs.getDouble("kilometer")));
}
rs.close();
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
return strecken;
}

First of all I would recommend that you use prepared statements while executing your queries instead of passing the query directly as a string......secondly I believe the problem here is that you are passing the date as a string in quotes and not a date.....I think that is the issue here. You would need to use sqllites datetime functions for this....

Unable to fix the error while inserting records into database using JDBC

public class StudentDataPersistence {
public void insertStudentInfo(Student student) {
String url = "jdbc:oracle:thin:#localhost:1521:XE";
String username = "system";
String password = "Data03#";
Connection connection = null;
//Statement statement = null;
try {
//Step 1 : Register JDBC driver
Class.forName("oracle.jdbc.driver.OracleDriver");
//Step 2 : Open a connection
System.out.println("Connecting to a selected database...");
connection = DriverManager.getConnection(url, username, password);
if (connection != null) {
System.out.println("Connected to oracle");
}
//Step 3 : Write code to map Java Object to the Student_Info table
System.out.println("Inserting records into the database");
statement = connection.createStatement();
String sql = "insert into Student_Info " +
"VALUES(student.getName(),student.getRoll_no(),student.getAddress(),student.getPhone_no())";
statement.executeUpdate(sql);
System.out.println("Inserted student information into the database");
} catch (SQLException se) {
//handle errors for JDBC
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
//Handle errors for Class.forName
} finally {
System.out.println("Inside the finally block");
//finally block used to close resources
try {
statement.close();
} catch (SQLException se) {
se.printStackTrace();
}
try {
connection.close();
} catch (SQLException se) {
se.printStackTrace();
}
}
System.out.println("!GoodBye");
}
public static void main(String[] args) {
Student student = new Student("Bavin", 1, "Umar Nagar", "89898989809");
StudentDataPersistence obj = new StudentDataPersistence();
obj.insertStudentInfo(student);
}
}
The error it shows it :
Connecting to a selected database...
Connected to oracle
Inserting records into the database
java.sql.SQLException: ORA-00904: "STUDENT"."GETPHONE_NO": invalid identifier
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:189)
at oracle.jdbc.ttc7.TTIoer.processError(TTIoer.java:242)
at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:554)
at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1478)
at oracle.jdbc.ttc7.TTC7Protocol.parseExecuteFetch(TTC7Protocol.java:888)
at oracle.jdbc.driver.OracleStatement.executeNonQuery(OracleStatement.java:2076)
at oracle.jdbc.driver.OracleStatement.doExecuteOther(OracleStatement.java:1986)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:2697)
at oracle.jdbc.driver.OracleStatement.executeUpdate(OracleStatement.java:1035)
at org.core.hibernate.reason.StudentDataPersistence.insertStudentInfo(StudentDataPersistence.java:52)
at org.core.hibernate.reason.StudentDataPersistence.main(StudentDataPersistence.java:80)
Inside the finally block
!GoodBye
All the answers (those of you who illustrate it with an oracle query) in reply were wrong.
Kindly do have a look at it before posting.
the correct one i got when i posted another thread regarding the same:
String query = "insert into Student_Info(name,roll_no,address,phone_no) VALUES('"+student.getName()+"',"+student.getRoll_no()+",'"+student.getAddress()+"','"+student.getPhone_no()+"')";

you have commented out your Statement object definition. So the statement object is unknown when you're using it.
uncomment this line:
//Statement statement;
And as earlier pointed out by #putaro, you need to quote certain parts of your SQL query.
String sql = "insert into Student_Info " +
"VALUES("+student.getName()+","+student.getRoll_no()+","+student.getAddress()+","+student.getPhone_no()+")";
This is to insert the actual object values into the query. Things within the quote would be inserted as it is.

Error ORA-00904 means Oracle does not know the identifier "STUDENT"."GETPHONE_NO" it looks like you are trying to insert some value to a column named "GetPhone_NO" to Table "Student" from your SQL. so you should check your SQL and table structure again

I see there are two problems in the code.
Currently your code is not using the student object while making the query. All student.getName() etc call taken as plain strings rather than method calls that returns the appropriate values.
Second it would be better to write the query in the following form. It will avoid silly errors because of the structure of the tables.
"INSERT INTO student_info(name,roll_no,address,phone) VALUES("+
student.getName()+"," +
student.getRoll_no()+","+student.getAddress()+","+student.getPhone_no()+")";
Even better is if you use prepared statement like
Try changing the query like
"INSERT INTO student_info(name,roll_no,address,phone) VALUES(?,?,?,?)"
and then set the parameter values.

Result set usage when expected one int value only

I know it is basics and probably really simple, but I'm struggling with the following situation where i want to query the database for a specific int(id in my case), but somehow i can't acces the returned data from the data set.
I have tested the query in db managment system and it works. I get no errors/ stacks but the result of my method is always -1.(Which means it fails :( because no int has been parsed)
code:
public int UserFactoryEngine(String n, String p){
// query for user data, validate and return
Connection conn = null;
try {
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver").newInstance();
} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
System.out.println("Failure intialization of the driver! ");
e.printStackTrace();
}
String connectionUrl = "jdbc:sqlserver://localhost:1433;" + "databaseName=BugsSurveillance;user=sa;password=1234;integratedSecurity=true;";
try {
conn = DriverManager.getConnection(connectionUrl);
} catch (SQLException e) {
System.out.println("Failure intialization of the connection! ");
e.printStackTrace();
}
System.out.println("Connected... ");
String sqlquery;
PreparedStatement preparedStatement;
ResultSet rs;
try {
preparedStatement = conn.prepareStatement("SELECT id FROM Users WHERE name = ? AND pass = ? ",
ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
preparedStatement.setString(1, n);
preparedStatement.setString(2, p);
rs = preparedStatement.executeQuery();
while (rs.next()){
System.out.println(rs.getInt(1));
}
} catch (SQLException e) {
System.out.println("Prepared statement failure!");
e.printStackTrace();
}
return -1;
}

You're not getting any output to the console from the
while (rs.next()){
System.out.println(rs.getInt(1));
}
because there are no results. Initially the ResultSet is pointed before the first row. When next() is called, it increments to the next row, and returns true only if the new current row is valid, which it must not be in this case.
Since you say the row exists, try replacing your lines
preparedStatement.setString(1, n);
preparedStatement.setString(2, p);
with hard coded values, for testing. So, if your username is admin, and your password is 1234.
preparedStatement.setString(1, "admin");
preparedStatement.setString(2, "1234");
Another test you could try is to
SELECT * FROM users
and see if you get any results that way.

Considering this is a login factory(what i'm trying to implement) i have been using a JPasswordField, which it seems needs a bit more atention when it comes to the getPassword() method. So because of that I wasen't able to succesfully find some matching string in database.
Fix: used JTextfield with hidden characters.

refactor JDBC function

I am trying to create a simple web app that saves user data from a form to a database and reads the content of the database back to browser upon request. Following are the functions I have written so far.
connectToDB() // connects to database
addEmployee() // adds employee to database
displayEmployee() // returns a resultSet
isExisted(int staffID) // checks if the staff already exists
Database connection function:
public void connectToDB(){
try{
// load Apache derby driver
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
} catch(ClassNotFoundException e) {
System.err.println(e);
}
try{
connection = DriverManager.getConnection(DBNAME, USERNAME, PASSWORD);
} catch(SQLException e){
System.err.println(e);
}
} // end connectToDB
Display Employee function:
public ResultSet displayEmployee(){
connectToDB();
ResultSet result = null;
try{
Statement stmt = connection.createStatement();
String query = "SELECT * FROM APP.ADDRESSBOOK";
result = stmt.executeQuery(query);
} catch(SQLException e) {
System.err.println(e);
}
return result;
}
Check if employee exists:
public boolean isExisted(int StaffID){
connectToDB();
try{
Statement stmt = connection.createStatement();
String query = "SELECT StaffNum FROM APP.ADDRESSBOOK WHERE StaffNum = " + staff_number;
ResultSet result = stmt.executeQuery(query);
while(result.next()){
int temp = result.getInt(1);
if(temp == staff_number){return true;}
}
} catch(SQLException e) {
System.err.println(e);
}
return false;
}
As you can see, if you compare the displayEmployee() and isExisted(), I am repeating mysel. Both the function works but I am looking to refactor the code. In those function I havent closed the connection. If there were 20 functions in the web app that connects to the database my code would stink.
I am looking something like this:
* THIS CODE DOESNT WORK ******
private Statement queryDB(query){
connectToDB();
Statement stmt;
try{
stmt = connection.createStatement();
} catch(SQLException e) {
System.err.println(e);
}
return stmt;
// code for closing connection
}
public ResultSet DisplayEmployee(){
String query = "SELECT * FROM APP.ADDRESSBOOK";
Statement stmt = queryDB(query);
ResultSet result = stmt.executeQuery(query);
return result;
}
Thanks.

Using raw JDBC produces a lot of unsightly boilerplate code. One solution is to use Spring JDBC Template.
In addition you will get the sql exception hierarchy which will manage the underlying JDBC exceptions automatically as runtime exceptions.
For more see:
Introduction to Spring Framework JDBC

A couple of comments:
The catch statement of ClassNotFoundException should throw an exception and shouldn't continue further.
It is not a good idea to return resultsets from a method that obtained them upon statement execution, since it is the responsibility of that method to close it. Instead, you should either read out the results into objects or cache them into CachedRowSet if your downstream functions expect a resultset.
The connectToDB method should return a successful connection or throw exception.
You could write a method that takes in an SQL query and return the results as objects so that this method can be used for retrieving based on different criteria as long you are retrieving the objects of same type.
isExisted is using staff_number which I think you intend it to be staffID. If you found a row with this value, then there is no need to check if the result set contained the row with this value, right?
My two cents!