Question

I have one demo application to check select for update query

public class Test implements Runnable{

    public Test() {
    }

    public static void main(String[] args) {
        Thread t1 = new Thread(new Test());
        Thread t2 = new Thread(new Test());

        t1.start();
        t2.start();
    }

    public void run() {
        // TODO Auto-generated method stub
        try{
            String updateWith = "";
            String sel = "SELECT SIDNUMBERTO FROM tblmserialbatchdetail WHERE sidnumberto = ("+
            "SELECT max(sidnumberto) FROM tblmserialbatchdetail WHERE generationmode='A' and nvl(serialprefix,' ') = nvl('',' ') " +
            "and sidlengthwithoutprefix =12) FOR UPDATE";
            //System.out.println("SELECT QUERY ===: "+sel);
            String updatequery = "update tblmserialbatchdetail set sidnumberto = ? where serialbatchid = ?";
            System.out.println();
            Connection connection = Conn.getDBConnection();
            PreparedStatement pStatement = connection.prepareStatement(sel);

            ResultSet rSet = pStatement.executeQuery();

            while(rSet.next()){

                updateWith = rSet.getString(1);
                long value = Long.parseLong(updateWith)+1;
                updateWith = String.valueOf(value);
                System.out.println("resulet To be Updated ===> "+value);
            }
            connection.commit();
            connection.close();



        }catch (Exception e) {
            e.printStackTrace();
        }
    }

}

This works fine if i remove For update from select query otherwise give me error

java.sql.SQLException: ORA-01002: fetch out of sequence

    at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:180)
    at oracle.jdbc.ttc7.TTIoer.processError(TTIoer.java:208)
    at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:543)
    at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1451)
    at oracle.jdbc.ttc7.TTC7Protocol.fetch(TTC7Protocol.java:943)
    at oracle.jdbc.driver.OracleStatement.doExecuteQuery(OracleStatement.java:2119)
    at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:2324)
    at oracle.jdbc.driver.OraclePreparedStatement.executeUpdate(OraclePreparedStatement.java:421)
    at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:365)
    at com.response.Test.run(Test.java:47)
    at java.lang.Thread.run(Thread.java:595)

Answer 1

SELCT ... FOR UPDATE only makes sense in the context of a managed transaction, since it requires locks to be taken out on the selected rows.

By default, JDBC does not use a managed transaction, it uses an implicitly created one that commits as soon as the query is executed. This will break the semantics of SELECT ... FOR UPDATE, and the JDBC driver complains.

In order to use a managed transaction, add

connection.setAutoCommit(false); 

before you execute the query. Afterwards, execute connection.commit().