Hey guys I'm trying to get the value from mySQL MAX function (trying to get highest customer ID) and store it in a variable in my java code. Can't seem to get the thing to work.
public static int findMaxID() {
int maxID = 0;
String updateStmt =
"SELECT #maxID := MAX(idCustomer)\n" +
"FROM customers\n";
try {
DBUtil.dbExecuteQuery(updateStmt);
System.out.println(maxID);
} catch (SQLException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return maxID;
}
Use a statement, ideally a prepared statement:
int maxID = 0;
String sql = "SELECT MAX(idCustomer) AS max_id FROM customers";
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
if (rs.next()) {
int maxID = rs.getInt("max_id"); // access the max value via its alias
}
While your current query might be valid MySQL, the session variable #maxID is only available on MySQL and not in your Java code. To access it you would need to yet again write another query.
I wrote some java code to display database, when I run the code it gives me just the last element of database , but I wanna display all elements of table
the code :
public String RecupererPuissance() {
try {
Connection con = myDbvoiture.getConnection();
String queryPattern ="select Power from bd_voiture";
PreparedStatement pstmt = con.prepareStatement(queryPattern);
ResultSet rs = pstmt.executeQuery();
while (rs.next()) {
puissance=rs.getString("Power");
System.out.println(puissance);
}
} catch (SQLException ex) {
System.err.println(ex.getMessage());
}
return puissance;
}
What should I do? Can anyone please help me to display all values?
Thank you for helping me.
I think the problem is with your code that the value of puissance is overwritten every time you get the next element. Only the last value is returned. You should put the results into a list and return the whole list:
public List<String> RecupererPuissance() {
List<String> puissances = new ArrayList<String>();
try {
Connection con = myDbvoiture.getConnection();
String queryPattern ="select Power from bd_voiture";
PreparedStatement pstmt = con.prepareStatement(queryPattern);
ResultSet rs = pstmt.executeQuery();
while (rs.next()) {
puissance = rs.getString("Power");
puissances.add(puissance);
System.out.println(puissance);
}
} catch (SQLException ex) {
System.err.println(ex.getMessage());
}
return puissances;
}
public String RecupererPuissance() {
try {
Connection con = myDbvoiture.getConnection();
String queryPattern ="select Power from bd_voiture";
PreparedStatement pstmt = con.prepareStatement(queryPattern);
ResultSet rs = pstmt.executeQuery();
rs.first();
int count=0;
while (rs.next()) {
System.out.println("count = "+count);
count+=1;
puissance=rs.getString("Power");
System.out.println(puissance);
}
} catch (SQLException ex) {
System.err.println(ex.getMessage());
}
return puissance;
}
If you see count printed only 1 time :
it would mean that you have only 1 row in column Power
and you maybe referring to the wrong column in your code
I am fetching next value of sequence with the ps = connection.prepareStatement("select seq.nextval from dual");
But neither getLong() nor getInt() works.
So how to correctly get the value from the ResultSet then?
full code:
public static long seqGetNextValue(String sequence) {
Connection connection = Util.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;
Long value = new Long(0);
try {
ps = connection.prepareStatement("select ? from dual");
ps.setString(1, sequence);
rs = ps.executeQuery();
if (rs.next()) {
value = rs.getInt(1);
}
System.out.println("Next payment Id: " + value);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
Util.close(connection, rs, ps);
}
return value;
}
The exception is below, for getInt it looks the same:
java.sql.SQLException: Fail to convert to internal representation
at oracle.jdbc.driver.CharCommonAccessor.getLong(CharCommonAccessor.java:258)
at oracle.jdbc.driver.T4CVarcharAccessor.getLong(T4CVarcharAccessor.java:562)
at oracle.jdbc.driver.GeneratedStatement.getLong(GeneratedStatement.java:228)
at oracle.jdbc.driver.GeneratedScrollableResultSet.getLong(GeneratedScrollableResultSet.java:620)
at org.apache.tomcat.dbcp.dbcp.DelegatingResultSet.getLong(DelegatingResultSet.java:228)
at org.apache.tomcat.dbcp.dbcp.DelegatingResultSet.getLong(DelegatingResultSet.java:228)
at util.Util.seqGetNextValue(Util.java:85)
PreparedStatements cannot bind object names, just values. If you attempt to bind seq.nextval as you're doing above, you're actually binding the string literal 'seq.nextval', so your code is effective doing the following:
SELECT 'seq.nextval' -- Note that this is a string!
FROM dual
Now it's obvious why getInt and getLong don't work - you aren't querying a number.
TL;DR - you cannot bind a sequence's name, and should just hard-code it in the statement (or use string manipulation/concatination to create the query). Once you've done that, you can use either getInt or getLong, depending on the values you expect to get. E.g.:
try {
ps = connection.prepareStatement("select " + sequence + " from dual");
rs = ps.executeQuery();
if (rs.next()) {
value = rs.getInt(1);
}
System.out.println("Next payment Id: " + value);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
Util.close(connection, rs, ps);
}
I am building an application in which you can save deals to database. I'd like to search deals in my database and populate my jtable with relevant results. I want to query my database on keyrelease event. I know it is not an efficient method but I am curious why I can't get it to work.
Below is a sample code that tries to query a database table with ID and country names. There are only 3 country names that start with "D". Somehow I can get country names printed out but can't get them to populate jtable.
The error -
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException" I can't get ResultSet rs1 into a Object[][] . It works fine if I do System.out.println(rs1.getString("Name")
Below is the code -
private void jTextField1KeyReleased(java.awt.event.KeyEvent evt) {
String columnName[] = new String[] { "Name" };
Object oss[][] = new Object[3][];
ResultSet rs1 = null;
int li = 0;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
java.sql.Connection con = DriverManager.getConnection(Url, User, Password);
Statement st = con.createStatement();
String query = "SELECT * from unit.cntry WHERE Name LIKE '" + abc.getText() + "%';";
rs1 = st.executeQuery(query);
} catch (Exception e) {}
try {
while (rs1.next()) {
oss[li][0] = rs1.getString("Name");
li++;
}
myTable.setModel(new DefaultTableModel(oss, columnName));
} catch (SQLException ex) {
System.out.println(ex.toString());
} finally {
try {
if (rs1 != null) rs1.close();
} catch (SQLException e) {}
}
}
oss[li] = new Object[1];
oss[li][0] = rs1.getString("Name");
Other data structures might be more appealing.
I've connected to a MySQL database, which contains four fields (the first of which being an ID, the latter ones each containing varchar strings).
I am trying to get the last row of the database and retrieve the contents of the fields so that I can set them to variables (an int and three strings) and use them later.
So far, I have the bare minimum to make the connection, where do I go from here? As you can see I have tried to write a SQL statement to get the last row but it's all gone wrong from there and I don't know how to split it into the separate fields.
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/t", "", "");
Statement st = con.createStatement();
String sql = ("SELECT * FROM posts ORDER BY id DESC LIMIT 1;");
st.getResultSet().getRow();
con.close();
Here you go :
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost/t", "", "");
Statement st = con.createStatement();
String sql = ("SELECT * FROM posts ORDER BY id DESC LIMIT 1;");
ResultSet rs = st.executeQuery(sql);
if(rs.next()) {
int id = rs.getInt("first_column_name");
String str1 = rs.getString("second_column_name");
}
con.close();
In rs.getInt or rs.getString you can pass column_id starting from 1, but i prefer to pass column_name as its more informative as you don't have to look at database table for which index is what column.
UPDATE : rs.next
boolean next()
throws SQLException
Moves the cursor froward one row from its current position. A
ResultSet cursor is initially positioned before the first row; the
first call to the method next makes the first row the current row; the
second call makes the second row the current row, and so on.
When a call to the next method returns false, the cursor is positioned
after the last row. Any invocation of a ResultSet method which
requires a current row will result in a SQLException being thrown. If
the result set type is TYPE_FORWARD_ONLY, it is vendor specified
whether their JDBC driver implementation will return false or throw an
SQLException on a subsequent call to next.
If an input stream is open for the current row, a call to the method
next will implicitly close it. A ResultSet object's warning chain is
cleared when a new row is read.
Returns:
true if the new current row is valid; false if there are no more rows Throws:
SQLException - if a database access error occurs or this method is called on a closed result set
reference
Something like this would do:
public static void main(String[] args) {
Connection con = null;
Statement st = null;
ResultSet rs = null;
String url = "jdbc:mysql://localhost/t";
String user = "";
String password = "";
try {
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection(url, user, password);
st = con.createStatement();
rs = st.executeQuery("SELECT * FROM posts ORDER BY id DESC LIMIT 1;");
if (rs.next()) {//get first result
System.out.println(rs.getString(1));//coloumn 1
}
} catch (SQLException ex) {
Logger lgr = Logger.getLogger(Version.class.getName());
lgr.log(Level.SEVERE, ex.getMessage(), ex);
} finally {
try {
if (rs != null) {
rs.close();
}
if (st != null) {
st.close();
}
if (con != null) {
con.close();
}
} catch (SQLException ex) {
Logger lgr = Logger.getLogger(Version.class.getName());
lgr.log(Level.WARNING, ex.getMessage(), ex);
}
}
}
you can iterate over the results with a while like this:
while(rs.next())
{
System.out.println(rs.getString("Colomn_Name"));//or getString(1) for coloumn 1 etc
}
There are many other great tutorial out there like these to list a few:
http://www.vogella.com/articles/MySQLJava/article.html
http://www.java-samples.com/showtutorial.php?tutorialid=9
As for your use of Class.forName("com.mysql.jdbc.Driver").newInstance(); see JDBC connection- Class.forName vs Class.forName().newInstance? which shows how you can just use Class.forName("com.mysql.jdbc.Driver") as its not necessary to initiate it yourself
References:
http://zetcode.com/databases/mysqljavatutorial/
This should work, I think...
ResultSet results = st.executeQuery(sql);
if(results.next()) { //there is a row
int id = results.getInt(1); //ID if its 1st column
String str1 = results.getString(2);
...
}
Easy Java method to get data from MySQL table:
/*
* CREDIT : WWW.CODENIRVANA.IN
*/
String Data(String query){
String get=null;
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = (Connection)DriverManager.getConnection
("jdbc:mysql://localhost:3306/mysql","root","password");
Statement stmt = (Statement) con.createStatement();
ResultSet rs=stmt.executeQuery(query);
if (rs.next())
{
get = rs.getString("");
}
}
catch(Exception e){
JOptionPane.showMessageDialog (this, e.getMessage());
}
return get;
}
Here is what I just did right now:
import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.sun.javafx.runtime.VersionInfo;
public class ConnectToMySql {
public static ConnectBean dataBean = new ConnectBean();
public static void main(String args[]) {
getData();
}
public static void getData () {
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/mynewpage",
"root", "root");
// here mynewpage is database name, root is username and password
Statement stmt = con.createStatement();
System.out.println("stmt " + stmt);
ResultSet rs = stmt.executeQuery("select * from carsData");
System.out.println("rs " + rs);
int count = 1;
while (rs.next()) {
String vehicleType = rs.getString("VHCL_TYPE");
System.out.println(count +": " + vehicleType);
count++;
}
con.close();
} catch (Exception e) {
Logger lgr = Logger.getLogger(VersionInfo.class.getName());
lgr.log(Level.SEVERE, e.getMessage(), e);
System.out.println(e.getMessage());
}
}
}
The Above code will get you the first column of the table you have.
This is the table which you might need to create in your MySQL database
CREATE TABLE
carsData
(
VHCL_TYPE CHARACTER(10) NOT NULL,
);
First, Download MySQL connector jar file, This is the latest jar file as of today [mysql-connector-java-8.0.21].
Add the Jar file to your workspace [build path].
Then Create a new Connection object from the DriverManager class, so you could use this Connection object to execute queries.
Define the database name, userName, and Password for your connection.
Use the resultSet to get the data based one the column name from your database table.
Sample code is here:
public class JdbcMySQLExample{
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/YOUR_DB_NAME?useSSL=false";
String user = "root";
String password = "root";
String query = "SELECT * from YOUR_TABLE_NAME";
try (Connection con = DriverManager.getConnection(url, user, password);
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query)) {
if (rs.next()) {
System.out.println(rs.getString(1));
}
} catch (SQLException ex) {
System.out.println(ex);
}
}