i have a server that backup the db and send me every time the db...
btw bc i don't want every time send 50mb of db i did a small program with something like
delete from table where timestamp < ?
get the last timestamp of the db and save it for the next backup
in that way i can send only the newest data (few kb instead 50mb)
now i want make another program for merge the different backups ...
i'm "stucked" on the insert part...
public static void merge(String toMerge) {
Connection c, c2 = null;
Statement stmt, stmt2 = null;
try {
Class.forName("org.sqlite.JDBC");
c = DriverManager.getConnection("jdbc:sqlite:merge.db");
System.out.println("Opened merge.db database successfully");
c.setAutoCommit(false);
stmt = c.createStatement();
c2 = DriverManager.getConnection("jdbc:sqlite:" + toMerge);
System.out.println("Opened " + toMerge + " database successfully");
stmt2 = c2.createStatement();
ResultSet rs = stmt2.executeQuery("SELECT * FROM messages;");
String sql;
while (rs.next()) {
sql = "INSERT INTO messages";
stmt.executeUpdate(sql);
}
rs.close();
stmt2.close();
c2.close();
stmt.close();
c.commit();
c.close();
} catch (Exception e) {
System.err.println(e.getClass().getName() + ": " + e.getMessage());
System.exit(0);
}
System.out.println("Operation done successfully");
}
i was thinking on open 2 db... 1 have a standard name "merge.db" (in that way i can merge 2+ db) and the other is the one to merge...
for use this method i open 2 connection (1 for each db) and read every line from db2 and insert in the new db... but here i have a few problem
the db have lots of cols so i need to use 200 getInt/String/Float
i have NULL value
i have a lot of rows
so if i use this method it require a lot of vars and time for make the insert query...
(for now i'm writing this method but if there is a simpler way for do it is better... i was thinking make a class with all the vars and use it for create the sql insert.. in that way i can use the same function for different tables (just need to extend the class for other class))
edit
in the table i have blob real int string values (29 cols in total)
If you had two tables in the same database, you could use a statement like this:
INSERT INTO messages1 SELECT * FROM messages2
When you have two different database files, you can ATTACH one to the other:
ATTACH DATABASE '...' AS toMerge
and then access it by prefixing the table name with the database name:
INSERT INTO messages SELECT * FROM toMerge.messages
Related
This is the code where I'm trying to execute a second query on the resultSet of my first lengthy query. I need to upload this
data somewhere.
Is it the right thing to do?
Or is there a better approach apart from querying the database again?
public String createQuery() throws SQLException {
StringBuilder Query = new StringBuilder();
try {
Query.append(" SELECT ...... ")
} catch (Exception e) {
e.printStackTrace();
}
return Query.toString();
}
private void openPreparedStatements() throws SQLException {
myQuery = createQuery();
try {
QueryStatement = dbConnection.prepareStatement(myQuery);
} catch (SQLException e) {
e.printStackTrace();
return;
}
}
public ResultSet selectData(String timestamp) throws SQLException {
openConnection();
ResultSet result = null;
ResultSet rs_new=null;
try {
result = QueryStatement.executeQuery();
while (result.next()) {
String query = "SELECT * FROM " + result + " WHERE " + "ID" + " =" + "ABC";
rs_new =QueryStatementNew.executeQuery(query);
System.out.print(rs_new);
}
} catch (SQLException e) {
LOGGER.info("Exception", e);
}
return result;
}
Instead of running two separate queries (when you don't need the intermediate one) you can combine them.
For example you can do:
SELECT *
FROM (
-- first query here
) x
WHERE ID = 'ABC'
You cannot use two statement objects within one database connection. So you can either open another database connection and execute the second statement in the 2nd connection, or iterate through the resultset from first statement and store the value you need (e.g. in an array/collection) then close that statement and run the second one, this time retrieving the value from the array/collection you saved them in. Refer to Java generating query from resultSet and executing the new query
Make Db2 keep your intermediate result set in a Global Temporary Table, if you have an ability to use it, and you application uses the same database connection session.
DECLARE GLOBAL TEMPORARY TABLE SESSION.TMP_RES AS
(
SELECT ID, ... -- Your first lengthy query text goes here
) WITH DATA WITH REPLACE ON COMMIT PRESERVE ROWS NOT LOGGED;
You may send the result of subsequent SELECT ... FROM SESSION.TMP_RES to FTP, and the result of SELECT * FROM SESSION.TMP_RES WHERE ID = 'ABC' to elastic.
I am writing a set of Eclipse console-based word games and have integrated an embedded Derby DB driver for storing a users result history.
My question is regarding Derby table initialization.
The Derby Database connection itself has a condition checker:
"jdbc:derby:dbName;create=true" So if the DB exists, it connects, if not it creates.
I am stuck on how to do this with a TBL in the Database. Even with the help from this similar question: how to create table if it doesn't exist using Derby Db
I've included my code below. My code throws a sql exception at the query for the Table 'RPS'. (My dbName is 'RPSdb' and TBL name is 'RPS'.)
This exception is caught by my catch block and passed to a static method in a different class ('DerbyHelper'). This static method is setup right now to always return true for the time being.
My question is how to I code my catch block and corresponding helper class so that I can implement the above mentioned TBL functionality?
Connection conn = null;
ArrayList<Statement> statements = new ArrayList<Statement>(); // list of Statements, PreparedStatements
Statement s;
ResultSet rs = null;
try {
conn = DriverManager.getConnection(protocol + dbName + ";create=true");
conn.setAutoCommit(false);
s = conn.createStatement();
statements.add(s);
rs = s.executeQuery("select * from RPS");
rs.next();
int cG = rs.getInt(1) + corGuess;
int iCG = rs.getInt(2) + inCorGuess;
s.executeUpdate("UPDATE RPS SET corGuesses = " + cG
+ ", inCorGuesses= " + iCG);
conn.commit();
}
catch( SQLException e ) {
if( DerbyHelper.tableAlreadyExists( e ) ) {
// what do I do here??
}
}
Interface java.sql.Connection has method getMetaData() which returns java.sql.DatabaseMetaData and that interface contains method getTables() which will tell you whether your database table exists, or not.
I am trying to add records to a table in an HSQL database through Java.
I have an HSQL database I made through OpenOffice, renamed the .odb file to .zip and extracted the SCRIPT and PROPERTIES files (It has no data in it at the moment) to a folder "\database" in my java project folder.
The table looks like this in the SCRIPT file
CREATE CACHED TABLE PUBLIC."Season"("SeasonID" INTEGER GENERATED BY DEFAULT AS IDENTITY(START WITH 0) NOT NULL PRIMARY KEY,"Year" VARCHAR(50))
All fine so far, the database connects just fine in Java with this code:
public void connect(){
try{
String dbName = "database\\db";
con = DriverManager.getConnection("jdbc:hsqldb:file:" + dbName, // filenames prefix
"sa", // user
""); // pass
}catch (Exception e){
e.printStackTrace();
}
}
I have the following code to insert a record into "Season".
public void addSeason(String year){
int result = 0;
try {
stmt = con.createStatement();
result = stmt.executeUpdate("INSERT INTO \"Season\"(\"Year\") VALUES ('" + year + "')");
con.commit();
stmt.close();
}catch (Exception e) {
e.printStackTrace();
}
System.out.println(result + " rows affected");
}
I have a final function called printTables():
private void printTables(){
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM \"Season\"");
System.out.println("SeasonID\tYear");
while(rs.next()){
System.out.println(rs.getInt("SeasonID") + "\t\t" + rs.getString("Year"));
}
}catch (Exception e) {
e.printStackTrace(System.out);
}
}
Now if I run this sequence of functions:
connect();
printTables();
addSeason("2010");
printTables();
I get this output:
SeasonID Year
1 rows affected
SeasonID Year
0 2010
Now when I close the program and start it again I get exactly the same output. So the change made during the first run hasn't been saved to the database. Is there something I'm missing?
It's caused by write delay params in hsqldb, by default has 500ms delay synch from memory to files.
So problem is solved when it's set to false
statement.execute("SET FILES WRITE DELAY FALSE");
or set as you like based on your app behaviour.
So my workaround is to close the connection after every update, then open a new connection any time I want to do something else.
This is pretty unsatisfactory and i'm sure it will cause problems later on if I want to perform queries mid-update. Also it's a time waster.
If I could find a way to ensure that con.close() was called whenever the program was killed that would be fine...
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);
}
I am trying to execute a BULK INSERT statement on SQL Server 2008 Express.
(It basically takes all fields in a specified file and inserts these fields into appropriate columns in a table.)
Given below is an example of the bulk insert statement--
BULK INSERT SalesHistory FROM 'c:\SalesHistoryText.txt' WITH (FIELDTERMINATOR = ',')
Given below is the Java code I am trying to use (but its not working)...Can someone tell me what I am doing wrong here or point me to a java code sample/tutorial that uses the Bulk Insert statement? --
public void insertdata(String filename)
{
String path = System.getProperty("user.dir");
String createString = "BULK INSERT Assignors FROM " + path + "\\" +filename+ ".txt WITH (FIELDTERMINATOR = ',')";
try
{
// Load the SQLServerDriver class, build the
// connection string, and get a connection
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
String connectionUrl = "jdbc:sqlserver://arvind-pc\\sqlexpress;" +
"database=test01;" +
"user=sa;" +
"password=password1983";
Connection con = DriverManager.getConnection(connectionUrl);
System.out.println("Connected.");
// Create and execute an SQL statement that returns some data.
String SQL = "BULK INSERT dbo.Assignor FROM " + path + "\\" +filename+ ".txt WITH (FIELDTERMINATOR = ',')";
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(SQL);
// Iterate through the data in the result set and display it.
while (rs.next())
{
//System.out.println(rs.getString(1) + " " + rs.getString(2));
System.out.println(" Going through data");
}
}
catch(Exception e)
{
System.out.println(e.getMessage());
System.exit(0);
}
}
I'd guess that your SQL string is missing the single quotes around the filename. Try the following:
String SQL = "BULK INSERT dbo.Assignor FROM '" + path + "\\" +filename+ ".txt' WITH (FIELDTERMINATOR = ',')";
EDIT in response to your comment: I wouldn't expect there to be anything in the ResultSet following a bulk insert, in much the same way that I wouldn't expect anything in a ResultSet following an ordinary INSERT statement. These statements just insert the data they are given into a table, they don't return it as well.
If you're not getting any error message, then it looks like your bulk insert is working. If you query the table in SQLCMD or SQL Server Management Studio, do you see the data?
INSERT, UPDATE, DELETE and BULK INSERT statements are not queries, so you shouldn't be using them with the executeQuery() method. executeQuery() is only intended for running SELECT queries. I recommend using the executeUpdate(String) method instead. This method returns an int, which is normally the number of rows inserted/updated/deleted.