I have the following work on my application, in which I am trying to update the value total on my mysql database table called "porcobrar2012". However, the only value that gets updated is the last one generated in the while loop. Why? all values are been printout on the screen with no problem, but those values are not getting updated in the database.
Here is the code:
BigDecimal total = new BigDecimal("0");
try
{
//Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
//Connection connection=DriverManager.getConnection("jdbc:odbc:db1","","");
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection connection=DriverManager.getConnection("jdbc:mysql://localhost/etoolsco_VecinetSM?user=etoolsco&password=g7Xm2heD41");
Statement statement=connection.createStatement();
String query;
query="SELECT * FROM porcobrar2012";
ResultSet resultSet=statement.executeQuery(query);
while(resultSet.next())
{
out.println(resultSet.getString(2)+"");out.println(resultSet.getBigDecimal(3)+"");out.println(resultSet.getBigDecimal(4)+"");out.println(resultSet.getBigDecimal(5)+"");out.println(resultSet.getBigDecimal(6)+"");out.println(resultSet.getBigDecimal(7)+"");out.println(resultSet.getBigDecimal(8)+"");out.println(resultSet.getBigDecimal(9)+"");out.println(resultSet.getBigDecimal(10)+"");out.println(resultSet.getBigDecimal(11)+"");out.println(resultSet.getBigDecimal(12)+"");out.println(resultSet.getBigDecimal(13)+"")out.println(resultSet.getBigDecimal(14)+"");out.println(resultSet.getBigDecimal(15)+"");
total = resultSet.getBigDecimal(3).add(resultSet.getBigDecimal(4)).add(resultSet.getBigDecimal(5)).add(resultSet.getBigDecimal(6)).add(resultSet.getBigDecimal(7)).add(resultSet.getBigDecimal(8)).add(resultSet.getBigDecimal(9)).add(resultSet.getBigDecimal(10)).add(resultSet.getBigDecimal(11)).add(resultSet.getBigDecimal(12)).add(resultSet.getBigDecimal(13)).add(resultSet.getBigDecimal(14)).add(resultSet.getBigDecimal(15));
String query1;
query1="UPDATE porcobrar2012 SET total=total";
PreparedStatement ps = connection.prepareStatement(query1);
ps.executeUpdate();
out.println(total);
}
connection.close();
statement.close();
}
catch (Exception e)
{
//e.printStackTrace();
out.println(e.toString());
}
It's because the update closes the existing result set. But I would ask why you aren't doing the addition in a single UPDATE statement without any prior query, at the database, no loops, no BigDecimals. Rule one of database programming is 'don't move the data further than you need to'. It would be many times as efficient to just write "UPDATE porcobrar2012 SET a=b+c+d+...". And you can remove the Class.forName() call too: it hasn't been required for years.
Related
My problem is that in a table of my database with 7 columns, I have a column of date type, called "Fecnac". Through MYSQLworkbrench, I execute a simple query:
"SELECT * FROM tblAsegurados ORDER BY Name,Nss"
As a result of this query, the information of my columns or fields of the table is displayed, the table contains a column named "Fecnac" that shows the correct date, for example "2018-12-31".
MYSQLworkbrench Result image
However, I developed an application in intelliJ IDEA to execute the same query, and the query "by itself" returns the date with one day less, that is, it shows "2018-12-30". And so it does with all the dates found in the "Fecnac" column of the "tblAsegurados" table in my database.
public ArrayList<Asegurados> getAseguradosList(){
ArrayList<Asegurados> aseguradosList = new ArrayList<Asegurados>();
Connection connection = getConnection();
var query = "select * from tblAsegurados order by Nombre,Nss";
Statement st;
ResultSet rs;
try{
st = connection.createStatement();
rs = st.executeQuery(query);
Asegurados asegurado;
while(rs.next()){
asegurado = new Asegurados(
rs.getString("Nss"),
rs.getString("Nombre"),
rs.getString("Curp"),
rs.getBoolean("Esposa"),
rs.getInt("Semcot"),
rs.getInt("Hijos"),
rs.getDate("Fecnac"));
aseguradosList.add(asegurado);
System.out.println(asegurado.getFecnac());
System.out.println(rs.getDate("Fecnac"));
System.out.println(rs.getDate(7));
}
} catch (Exception e){
e.printStackTrace();
}
return aseguradosList;
}
The class "Asegurados" has an attribute of type "java.sql.date" defined, to receive "rs.getdate (Fecnac).
For i be sure of the values returned by the query, in my code you can see that I made a "System.out.println" for each field date, and in all three I get the same value from the date with one day less.
Could someone help me know what happens?
Console debug IntelliJ Idea image
I already found the solution. In a part of my code, the parameter of the time zone had it defined as: serverTimezone = UTC
public static Connection getMySQLConnection() throws Exception {
String driver = "com.mysql.cj.jdbc.Driver";
String url = "jdbc:mysql://localhost/imss"+
"?useUnicode=true&useJDBCCompliantTimezoneShift=true"+
"&useLegacyDatetimeCode=false&serverTimezone=America/Mexico_City"+
"&verifyServerCertificate=false"+
"&useSSL=true"+
"&requireSSL=true";
String username = "root";
String password = "juan1980";
Class.forName(driver);
return DriverManager.getConnection(url, username, password);
}
I set it to: serverTimezone = america / Mexico_City, which is the zone that corresponds to me, and ready! the date is displayed correctly.
Hi i have this managed bean where it makes MySQL queries, the problem here is the SQL statement makes a '=' condition instead of 'LIKE'
Here is the code in my managed bean.
Connection con = ds.getConnection();
try{
if (con == null) {
throw new SQLException("Can't get database connection");
}
}
finally {
PreparedStatement ps = con.prepareStatement(
"SELECT * FROM Clients WHERE Machine LIKE '53'");
//get customer data from database
ResultSet result = ps.executeQuery();
con.close();
List list;
list = new ArrayList();
while (result.next()) {
Customer cust = new Customer();
cust.setMachine(result.getLong("Machine"));
cust.setCompany(result.getString("Company"));
cust.setContact(result.getString("Contact"));
cust.setPhone(result.getLong("Phone"));
cust.setEmail(result.getString("Email"));
//store all data into a List
list.add(cust);
}
return list;
Here the SELECT command does not pull all the numbers in 'Machine' column which is like 53, but if i enter a whole value, such as the complete number (53544) in place of 53 then the result is pulled up. I am confused !!
Also if i replace the above select statement with SELECT * FROM Clients the entire database is stored in list. Any ideas ?
Use wildcards:
Like '%53%'
...means everything that contains '53'.
Like '%53' - it ends with 53
LIKE '53%' - it starts with 53
You can also use _ if You want to replace a single character.
You can find a descriptipn HERE
You sql query should be
"SELECT * FROM Clients WHERE Machine LIKE '%53%'
I want to make several entries into a MySQL database. Because Some of the tables reference others via foreign key I have to get back the inserted ID to inject them in my next statements.
I have 4 classes:
LodgerFormTest
RentForm
RentObject
House
and the class which inserts the MySQL statements into the db: sql_statements
When I want to send a SQL statement I am getting a nullPointer Exception!
The Action listener of the House-class (this is the first sql-statement I have to send) looks like this:
saveButton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
System.out.println("saveButton");
// sql_statements statements = new sql_statements();
sql_statements.performHouse(strasse.getText(), plz.getText(), ort.getText());
mainmenu.create();
rentnerFrame.dispose();
}
});
all methods and variables I am using in sql_statements are static! Therefore I am not instantiating an object.
here is the method "performHouse" in sql_statements
public static void performHouse(String strasse, String plz, String ort) {
String sql = "insert into haus(strasse, plz, ort) values (?,?,?)";
System.out.println(sql);
try{
ps = connect.prepareStatement(sql, ps.RETURN_GENERATED_KEYS);
ps.setString(1, strasse);
ps.setString(2, plz);
ps.setString(3, ort);
ps.execute();
rs = ps.getGeneratedKeys();
if(rs != null && rs.next()) {
// Retrieve the auto generated key(s).
key_idhaus = rs.getLong(1);
System.out.println("idhaus: " + key_idhaus);
}
}catch(Exception ex){
System.out.println(ex);
}
} // close performHouse-methode
I cant debug because I get a "Source not found." error in the debug view.
Can anybody help please?
okay I just wanted to finish the task so I implemented a solution which surely is all but not OO:
I implemented redundant code into all of the 4 classes and every class implements their own sql statements. quick and dirty ;)
hello guys i am try to validate username from the database with the username that the user entered in the html from, assume
un//be the variable where username entered now from html form is stored
now how to retrieve all the columns of the uname from user table
uname //column name in mysql for usernames
user //table name in mysql
and check weather the username i.e,un entered now is present or not in the database
i am using
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/mebps","root","admin");
Statement stmt = (Statement) con.createStatement();
ResultSet rs = stmt.executeQuery("select un from userinfo");
while(rs.next())
{
if(rs.getString("uname") == un)
{
out.println("user is present");
}
}
There are at least two major mistakes:
You're comparing string instances by == instead of comparing their values by equals() method. The proper line would be if (rs.getString("uname").equals(un)).
You're not letting the DB do the job of returning the right row, instead you're copying the entire DB table into Java's memory and doing the comparison in Java. This is very inefficient. Make use of SQL powers the smart way so that it always returns exactly the information you need. There's for example a WHERE clause.
On an unrelated note, you seem not to be closing DB resources properly after use. This will result in resource leaking which is also a bad idea as it may cause your application to crash on long term. Further, the column name uname and un are not the same. But I'll assume it to be careless oversimplifying of the example.
Here's a minor rewrite:
public boolean exist(String username) throws SQLException {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
boolean exist = false;
try {
connection = database.getConnection();
statement = connection.prepareStatement("SELECT uname FROM userinfo WHERE uname=?");
statement.setString(1, username);
resultSet = statement.executeQuery();
exist = resultSet.next();
} finally {
if (resultSet != null) try { resultSet.close(); } catch (SQLException ignore) {}
if (statement != null) try { statement.close(); } catch (SQLException ignore) {}
if (connection != null) try { connection.close(); } catch (SQLException ignore) {}
}
return exist;
}
You see, if there's a match, then it returns true (at least one record), otherwise false (no one record). No need to copy the entire table into Java's memory and crawl through it in Java.
Last but not least, this code doesn't belong in a JSP file, but in a normal Java class, starting with a servlet. See also our servlets wiki page to learn more about it.
There are 1652487 rows in my table in MYSQL. I want to copy all the values corresponding to one field into a file. I wrote a java program in netbeans using jdbc driver for this. I'm unable to do this at one go. Is there a way out ? < Is there any limit on the number of rows one can select >
[ EDIT ]
my code : action performed when a button is pressed :
private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
try
{
File fo=new File("D:\\dmoz_externalpages.txt");
FileWriter fro=new FileWriter(fo);
BufferedWriter bro=new BufferedWriter(fro);
Connection con=null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/dmozphp","root","");
PreparedStatement ps=con.prepareStatement("select externalpage from content_description");
ResultSet rs=ps.executeQuery();
while(rs.next())
{
bro.write(rs.getString(1));
bro.newLine();
bro.flush();
}
}
catch(Exception e)
{
System.out.println(e);
}
}
when i run this , i get the following exception :
Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: Java heap space
There is no MySQL limit on this. My strong guess is you're limited by the memory on the client side.
I've been able to export entire tables with >25mil rows without problems before.
If you want to export the data the quickest way, use SELECT INTO OUTFILE or give Maatkit a go.