I try to execute INSERT query in cycle:
String selectTableSQL = "SELECT * "
+ "FROM testTable";
ResultSet rs = stmt.executeQuery(selectTableSQL);
while (rs.next()) {
String rangeName = rs.getString("RANGENAME");
insertTableSQL = "INSERT INTO testTable2 "
+ "VALUES ('" + rangeName + "')";
try {
stmt.executeUpdate(insertTableSQL);
} catch (SQLException e) {
// do nothing
}
But after one iteration this cycle breaks. If I don't execute INSERT query and print rangeName to screen everything works perfectly (there are a lot of values, not only one). So the problem is in statement execution. How can I solve it?
Thank you very much!
Of course it does: you're using the same stmt
Create a new stmt2 variable and use it inside loop without destroying the previous one.
First: Never do so
} catch (SQLException e) {
// do nothing
}
Add a e.printStackTrace() to the catch block.
I think you get an exception when you do so. You may need a second statement variable.
Related
I am using mySQL. As you see, the SQL statement is wrong at SELECT. So, I wonder what value the rs is?
I hope to get some advice. I thank you so much;
String sql = "SELCT * FROM user WHERE username = '" + username + "' and password = '" + password + "'";
ResultSet rs = stm.executeQuery(sql);
There would be no value because Statement.executeQuery(String) would throw a SQLException. As the linked Javadoc says,
Returns:
a ResultSet object that contains the data produced by the given query; never null
Throws:
SQLException - if a database access error occurs, this method is called on a closed Statement, the given SQL statement produces anything other than a single ResultSet object, the method is called on a PreparedStatement or CallableStatement
It will return you an exception having message like syntax error.
Easiest way to find is to debug your code by putting break points in code & examining / watching values of variables . Most IDEs have these debugging features. In addition to Elliott Frisch's answer, if I restructure your code like below then in case of invalid / incorrect SQL, control comes to catch block and you can see that value of rs remains null.
public void executeQuery(Connection conn, String username,String password) {
String sql = "SELCT * FROM user WHERE username = '" + username + "' and password = '" + password + "'";
ResultSet rs = null;
Statement stm = null;
try {
stm = conn.createStatement();
rs= stm.executeQuery(sql);
while(rs.next()) {
//Extract ResultSet here as per needed logic
}
} catch (SQLException e) {
// Your control comes here if query is wrong , put a break point at below line & examine value of rs
e.printStackTrace();
}finally {
// Close resources not needed after this method call like - result sets , statements & connection
}
}
Firstly statement won't execute, so next execution is depends on how you are going to handle that exception. So, if exception comes and if you handle also there will be null in ResultSet because no value assigned to it.
try {
ResultSet rs = stat.executeQuery("select * from details where COURSEANDDEPT='"+username+"'");
//if (rs.next()) {
while (rs.next()) {
String logid=rs.getString(1);
char temp=' ';
ResultSet ag=stat.executeQuery("select type from login");
if (ag.next()) {
temp=ag.getString(1).charAt(0);
if (temp=='s' || temp=='S') {
String logid=ag.getString(1);
stat.executeQuery("insert into assignments values('"+logid+"','"+comments+"','P','"+userid+"','"+username+"')");
}
}
}
JOptionPane.showMessageDialog(this,"Assignment Sent To The Whole Class");
//} else {
//JOptionPane.showMessageDialog(this,"Invalid Branch");
//}
} catch (ClassNotFoundException | SQLException ex) {
Logger.getLogger(Assignments.class.getName()).log(Level.SEVERE, null, ex);
}
The while loop of rs.next() terminates only in one iteration even after containing 6 records in itself. How to rectify it?
The problem is that you use the same statement object for executing several queries. Addictional problems are
you don't close neither your statements neither your resultsets (see example).
you should use statements' parameters (see example).
you should not use select *, but list the columns you want back from statement (i'll not include this in the example).
one of the queries ("select type from login") is always repeated the same way, maybe there's an error on the query. Otherwise it should be executed once outside the main loop.
in the example i don't manage the connection but this should be done too
Lets suppose that you have a Connection object called conn
PreparedStatemet stat=null;
PreparedStatement innerStat=null;
PreparedStatement insertStat=null;
try {
stat=conn.prepareStatement("select * from details where COURSEANDDEPT=?");
stat.setString(1,username);
ResultSet rs = stat.executeQuery();
//if (rs.next()) {
while (rs.next()) {
String logid=rs.getString(1);
char temp=' ';
innerStat=conn.prepareStatement("select type from login");
ResultSet ag=innerStat.executeQuery();
if (ag.next()) {
temp=ag.getString(1).charAt(0);
if (temp=='s' || temp=='S') {
String logid=ag.getString(1);
ag.close();
innerStat.close();
insertStat=conn.prepareStatement("insert into assignments values(?,?,?,?,?)");
insertStat.setString(1,logId);
insertStat.setString(2,comments);
insertStat.setString(3,"P");
insertStat.setString(4,userid);
insertStat.setString(5,username);
insertStat.executeUpdate();
insertStat.close();
}//closes if on temp
} //closes if on ag
} //closes while
rs.close();
stat.close();
JOptionPane.showMessageDialog(this,"Assignment Sent To The Whole Class");
//} else {
//JOptionPane.showMessageDialog(this,"Invalid Branch");
//}
} catch (ClassNotFoundException | SQLException ex) {
Logger.getLogger(Assignments.class.getName()).log(Level.SEVERE, null, ex);
if(insertStat!=null) insertStat.close();
if(innerStat!=null) innertStat.close();
if(stat!=null) stat.close();
}
Your problem is that each connection can only handle one SQL statement at a time. You're trying to leave your first select statement open while you do a bunch of other statements. You can't do this on a single connection.
I suggest two changes to make this work.
Do the query against the login table first. Its result won't vary from one iteration to the next, so there is no point in repeating it over and over within the main loop.
Rewrite the queries against details and assignments as an insert/select statement. It's probably something like the following.
.
"insert into assignments " +
"select logid, ,'" + comments + "','P','" + userid + "','" + username + "' "
"from details " +
"where COURSEANDDEPT='"+username+"'"
Also, you might consider writing this with a PreparedStatement, depending on whether SQL injection attacks are a likelihood.
Some behaviour I don't understand.
I have a running script like:
ResultSet res = null;
String cmd = new String("SELECT value FROM " +pDS.getValueTableName() + " WHERE itemID=? and propertyID=? ORDER BY checkpointID DESC");
PreparedStatement pstmt= dbconn.prepareStatement(cmd) ;
pstmt.setLong(1,itemID);
pstmt.setLong(2,pDS.getPropertyID());
try {
res = pstmt.executeQuery();
}
catch(Exception e)
{
throw(e);
}
if (!res.next())
{
// other code
}
Here i get the expected values res.next()=true.
No exception is thrown.
I wanted to refactor the code, and use the Autoclose funtionalty of the try block, like:
ResultSet res = null;
String cmd = new String("SELECT value FROM " +pDS.getValueTableName() + " WHERE itemID=? and propertyID=? ORDER BY checkpointID DESC");
try (PreparedStatement pstmt= dbconn.prepareStatement(cmd) ){
pstmt.setLong(1,itemID);
pstmt.setLong(2,pDS.getPropertyID());
res = pstmt.executeQuery();
}
catch(Exception e)
{
LOGGER.error("Error at getLatestPropertyResultSet",e);
throw(e);
}
if (!res.next())
{
// other code
}
However now res.next()=false. The resultset itselve is intialized res!=null.
Why did this modification change the behaviour of the script?
Without seeing where you call res.next() I can only assume that the try-with-resource is doing exactly as advertised and closing the prepared statement once you leave the try block and thus the result is "closed" with it.
update: based on your edit my suspicions are confirmed. You need to move any work related to the resource inside the try block.
I am trying to update a table using Java JDBC. The method I am using does not throw any errors but the table is not updating. The create table method is below:
public static void Table()
{
Connection c = null;
Statement stmt = null;
try {
Class.forName("org.sqlite.JDBC");
c = DriverManager.getConnection("jdbc:sqlite:WalkerTechCars.db");
System.out.println("Opened database successfully");
stmt = c.createStatement();
String sql = "CREATE TABLE IF NOT EXISTS CUSTOMERS2 " +
"(PHONE TEXT PRIMARY KEY NOT NULL," +
" SURNAME TEXT NOT NULL, " +
" FIRSTNAME TEXT NOT NULL, " +
" HOME TEXT, " +
" ADDRESS TEXT, " +
" POSTCODE Text)";
stmt.executeUpdate(sql);
stmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName() + ": " + e.getMessage() );
System.exit(0);
}
System.out.println("Customers2 created successfully");
}
The update method is below:
public static void updateCustomers()
{
Connection c = null;
PreparedStatement pstmt = null;
try {
Class.forName("org.sqlite.JDBC");
c = DriverManager.getConnection("jdbc:sqlite:WalkerTechCars.db");
c.setAutoCommit(false);
System.out.println("Opened database successfully");
String query = "UPDATE CUSTOMERS2 set ADDRESS = ? where PHONE = ? ";
pstmt = c.prepareStatement(query); // create a statement
pstmt.setString(1, "1"); // set input parameter 1
pstmt.setString(2, "DOES THIS WORK"); // set input parameter 2
pstmt.executeUpdate(); // execute update statement
pstmt.close();
c.close();
} catch ( Exception e ) {
System.err.println( e.getClass().getName() + ": " + e.getMessage() );
System.exit(0);
}
System.out.println("Update Completed successfully HELLO");
}
I have tried to find some clear instructions on this but cant find any. I do not really understand JDBC and prepared statement very well
When autoCommit is false (c.setAutoCommit(false);), you must manually commit the transaction...
Add...
c.commit()
After pstmt.executeUpdate();
You code also has a flaw, in that if some kind of error occurs during the preparation or execution of the statement, both the Connection and PreparedStatement could be left open, causing a resource leak
If you're using Java 7+ you can use the try-with-resources feature, for example...
try {
Class.forName("org.sqlite.JDBC");
try (Connection c = DriverManager.getConnection("jdbc:sqlite:WalkerTechCars.db")) {
c.setAutoCommit(false);
System.out.println("Opened database successfully");
String query = "UPDATE CUSTOMERS2 set ADDRESS = ? where PHONE = ? ";
try (PreparedStatement pstmt = c.prepareStatement(query)) {
pstmt.setString(1, "1"); // set input parameter 1
pstmt.setString(2, "DOES THIS WORK"); // set input parameter 2
pstmt.executeUpdate(); // execute update statement
c.commit();
}
} catch (SQLException exp) {
exp.printStackTrace();
}
} catch (ClassNotFoundException exp) {
exp.printStackTrace();
System.out.println("Failed to load driver");
}
This will ensure that regardless of how you leave the try block the resource will be closed.
You might also consider taking a look at the JDBC(TM) Database Access
Your update method will set ADDRESS to 1 if there is any row in table with PHONE = does this work.
Try to put Address in 1st Input parameter and Phone 2nd Input parameter
When a connection is created, it is in auto-commit mode.
We need to use [setAutoCommit] method only when we need to make Auto Commit false and make it manual commit after executing the query.
More details at Oracle site on JDBC Transaction.
If I remove beforeFirst() my function does only first record in ResultSet and go to end. If I use beforeFirst() I get an error ResultSet IS_TYPE_FORWARD_ONLY.
try {
ResultSet rs = stat.executeQuery("select _id, godziny_id from tblZmiany where harmonogram_id = " + h_id + " order by pracownik_id, Dzien");
rs.beforeFirst();
while (rs.next()) {
if (stat.executeUpdate("insert into tblWykonanie (Zmiana_id, Godziny_id) values ('" + rs.getLong(1) + "', " + rs.getInt(2) + ");") < 1) {
// Jeśli insert nie wstawił kolejnego rekordu
error_code = "Wystąpił problem podczas zatwierdzania harmonogramu.";
return false;
}
}
} catch (SQLException e) {
e.printStackTrace();
System.out.println(e.getMessage());
return false;
} catch (Exception e) {
error_code = e.getMessage();
return false;
}
return true;
You're using the same Statement object for both the SELECT and the INSERT. From the Javadoc:
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.
To fix the problem, use a separate Statement object for the executeUpdate() call.
Also, I strongly advise you to change the code to use PreparedStatement with bound arguments (represented by ?). Building SQL statements bit by bit as you're doing right now could open up security vulnerabilities.
Your code has a major security flaw. You are vulnerable to SQL injection. Never, ever, ever, ever, ever, ever, ever, use string concatenation with SQL statements; use PreparedStatements instead!
harmonogram_id = " + h_id + " order by pracownik_id,
Take a look here to see how your application could be easily owned with simple tricks:
http://en.wikipedia.org/wiki/SQL_injection
To answer your question though, it depends on your database. You have to set a property during the connection creation:
Statement stmt = con.createStatement(
ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_UPDATABLE),
ResultSet.HOLD_CURSORS_OVER_COMMIT);
From:
http://docs.oracle.com/javase/1.4.2/docs/guide/jdbc/getstart/resultset.html#1012735