Develop Reference

Working on this Java project where I need to be able to delete data from the database on user's request

The query inside MySQL is working:
DELETE FROM f9.yoo
WHERE account_tags = '#8GGGJPUR9'
I can delete data inside MySQL, but the problem is whenever I try to remove the account_tags from my Java application, it throws an error:
java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DELETE FROM f9.yoo
WHERE account_tags = '#8GGGJPUR9'' at line 2
Here's my Java SQL query:
Statement statement = dbConnection.createStatement();
String sql = "SELECT * FROM "+databaseName+"."+tableName+";\n" +
"DELETE FROM "+databaseName+"."+tableName+"\n" +
"WHERE account_tags = '"+AccountTag+"';";
statement.executeQuery(sql);
The error isn't giving me much to work with, so I really have no idea what is wrong with the program.

Did you add the allowMultiQueries=true
If not then you can add that while you sending the connecting request to your database. So you need to append the allowMultiQueries=true in your to database URL.
Like this:
String dbUrl = "jdbc:mysql:///test?allowMultiQueries=true";

String sql = "DELETE FROM "+databaseName+"."+tableName+"\n" +
"WHERE account_tags = ?";
try (PreparedStatement statement = dbConnection.prepareStatement(sq)) {
statement.setString(1, AccountTag);
int updateCount = statement.executeUpdate();
System.out.printf("%s: %d records deleted.%n", tableName, updateCount);
}
The only thing used is the DELETE, for which one should use executeUpdate.
One definitely should use a PreparedStatement as many code checkers will give alarms otherwise. It escapes things like ', handles types of the arguments, and possible conversions, and especially is a security feature against SQL injection.
The System.out usage is bad style, better would be using a logger.
try-with-resources automatically closes the PreparedStatement even with a raised exception or break/return.
When doing both database operations, it seems better to use two (prepared) statements, as the first returns a ResultSet.
So:
String sql = SELECT * FROM "+databaseName+"."+tableName + "\n" +
"WHERE account_tags = ?";
try (PreparedStatement statement = dbConnection.prepareStatement(sq)) {
statement.setString(1, AccountTag);
try (ResultSet rs = statement.executeQuery()) {
...
}
}

Better to separate statements with an If condition :
String sql1="SELECT * FROM "+databaseName+"."+tableName;
String sql2="DELETE FROM "+databaseName+"."+tableName+" "+
"WHERE account_tags = '"+AccountTag+"';
statement.executeQuery(sql1);
statement.executeUpdate(sql2);

How do you get the values from a stored procedure in postgresql into a java application? I keep getting an error

I have created a stored procedure in my postgres database with a simple SELECT statement:
SELECT DISTINCT device FROM dev_op_test ORDER BY device;
In the java app I am trying to get the list of devices into the resultset:
// Get unique devices from table
String sql = " { ?= call sp_search_devices() }";
CallableStatement statement = pgConn.prepareCall(sql);
ResultSet rs = statement.executeQuery();
And I keep getting the following error:
Any ideas what I am doing wrong? The sp_search_devices() is not expecting any input parameters as it is just a pretty simple SELECT statement.

Ended up using:
CREATE OR REPLACE FUNCTION sp_search_test_ui_devices()
RETURNS SETOF text AS $$
SELECT DISTINCT device AS device FROM dev_op_test ORDER BY device;
$$ LANGUAGE SQL;
and
String sql = " SELECT sp_search_test_ui_devices() ";
PreparedStatement statement = pgConn.prepareStatement(sql);
ResultSet rs = statement.executeQuery();

Are ResultSet update{ColumnType} methods vulnerable to SQL injection?

A security scan made by AppScan source flags that the input has to be validated (Validation.Required) on the line uprs.updateString in the code below:
PreparedStatement statement =
conn.prepareStatement (query, ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
...
ResultSet uprs = statement.executeQuery ();
...
// Update DB ColumnA with input coming from client
uprs.updateString ('ColumnA', unvalidatedUserInput);
...
// Updates the underlying database
uprs.updateRow();
I assume that the intention behind this is to avoid SQL injection attacks, but I'm not sure whether that is possible in that scenario.
Questions: Are SQL Injection attacks possible through these JDBC methods? How does JDBC implements this under the scenes? Would this be another false positive reported by AppScan?

I'm not sure about bluemix-app-scan, but I'm providing my explanation here. (This is my assumption based on the below tests and code pasted)
I ran a test code to check this (in H2 DB)
value of testName String : (select 'sqlInjection' from dual)
Using createStatement (Not-Safe):
String query = "update TEST_TABLE set TEST_CHAR = " + testName + " where ID = 1";
Statement statement = connection.createStatement();
statement.executeUpdate(query);
Output: TEST_CHAR in DB was sqlInjection.
Using ResultSet of createStatement (Safe in H2 DB):
String query = "select * from TEST_TABLE where ID = 1";
Statement statement = connection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
ResultSet executeQuery = statement.executeQuery(query);
executeQuery.next();
executeQuery.updateString("TEST_CHAR", testName);
executeQuery.updateRow();
Output: Surprisingly TEST_CHAR in DB was (select 'sqlInjection' from dual).
Using PreparedStatement (Safe):
String query = "update TEST_TABLE set TEST_CHAR = ? where ID = 1";
PreparedStatement statement = connection.prepareStatement(query);
statement.setString(1, testName);
statement.executeUpdate();
Output: Expected - TEST_CHAR in DB was (select 'sqlInjection' from dual).
Using ResultSet of prepareStatement (Safe in H2 DB):
String query = "select * from TEST_TABLE where ID = 1";
PreparedStatement statement = connection.prepareStatement(query, ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = statement.executeQuery();
uprs.next();
uprs.updateString("TEST_CHAR", testName);
uprs.updateRow();
Output: Expected - TEST_CHAR in DB was (select 'sqlInjection' from dual).
Back to Questions:
Are SQL Injection attacks possible through these JDBC methods?
Maybe. It depends on the database driver that you're using.
How? :
The reason SQL Injection failed in my result set update was because H2 database internally uses PreparedStatement to update the row when ResultSet.updateRow() is invoked.
public void updateRow(Value[] current, Value[] updateRow) throws SQLException {
StatementBuilder buff = new StatementBuilder("UPDATE ");
...
buff.append(" SET ");
appendColumnList(buff, true);
...
appendKeyCondition(buff);
PreparedStatement prep = conn.prepareStatement(buff.toString());
...
for (int i = 0; i < columnCount; i++) {
...
v.set(prep, j++);
}
setKey(prep, j, current);
int count = prep.executeUpdate();
...
}
I'm not sure if all DB drivers in java implemented updateRow() method using preparedStatement or not. However it's clear that this is left to the driver and if bluemix is suggesting you to add a validation here, I suggest you follow that :)
How does JDBC implements this under the scenes?
Well, as shown above this is driver specific. However there is a good explanation on how PreparedStatement handles it over here.
Would this be another false positive reported by AppScan?
I don't think this is false positive (but in cases like H2 DB it is) but you'll never know if all database drivers implemented this securely.
Edit -
Even PostgreSQL and MySQL use PreparedStatement to handle this.
public synchronized void updateRow() throws SQLException
{
...
updateStatement = ((java.sql.Connection) connection).prepareStatement(updateSQL.toString());
...
updateStatement.executeUpdate();
...
}

Unknown column '$a' in 'where clause'

i want to fetch data from database by using a variable string.it shows error
"Unknown column '$a' in 'where clause'"
String a=request.getParameter("from");
ResultSet resultset= statement.executeQuery("select * from flight where f = $a") ;

If you want to use the value of the a variable where you have $a, you need to use a prepared statement and fill it in:
String a = request.getParameter("from");
PreparedStatement ps = connection.prepareStatement( // Create a prepared statement
"select * from flight where f = ?" // Using ? for where the
); // parameter goes
ps.setString(1, a); // Fill in the value (they
// start a 1, oddly)
ResultSet resultset = ps.executeQuery(); // Execute the query
Note that even though it's a string, you don't put quotes around the ?. The PreparedStatement handles that for you at the DB driver level, in a way that's safe from SQL injection.

SELECT * WHERE in H2 database

I'm trying to do in my program a JDBC connection with my Embedded H2 database. The problem is that I couldn't execute a simple query with "WHERE ID =". In my databse, the ID are string not integer ('D58BE' in my example).
There is my code :
public Milestone findbyId(String id) throws ClassNotFoundException, SQLException {
Class.forName("org.h2.Driver");
Connection connection = DriverManager.getConnection("jdbc:h2:~/dao_db", "sa", "");
PreparedStatement prepareStatement = connection.prepareStatement("SELECT * FROM MILESTONE WHERE ID= 'D58BE'");
The problem is that the SAME query ("SELECT * FROM MILESTONE WHERE ID= 'D58BE'") works perfectly in my embeded database (I verify the result with the h2.jar provided to manage the database). While in eclipse, I had this exception :
Exception in thread "main" org.h2.jdbc.JdbcSQLException: Column "D58BE" not found [42122-191]
I tried A LOT of things but it still never works...

To execute it directly, create a statement and execute your SQL:
Statement statement = connection.createStatement();
statement.executeQuery("SELECT * FROM MILESTONE WHERE ID= 'D58BE'");
You are using a prepared statement, so you need to use placeholders:
PreparedStatement statement = connection.prepareStatement("SELECT * FROM MILESTONE WHERE ID=?);
statement.setString(1, "D58BE");
statement.executeQuery();
EDIT
For a detailed example and also how to process a ResultSet, you can look at the following tutorial: https://docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
For your case it should be something along the lines of:
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
String id = rs.getString("ID");
String name = rs.getNamex("NAME"); // Assuming there is a column called name.
System.out.println(id);
}