Why this mysql find max value stament won't run in Java JDBC

Question

I have a table with column id, i want to select max value of id and +1 to that value because i'm running a loop. But the sql stament not work, but why? i have test it with mysql comand and it work well! Thank you!

Error: Exception in thread "main" java.sql.SQLException: Before start of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:959) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:862) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:790) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2469) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2580) at MyPackage.TestMax.main(TestMax.java:23) C:\Users\lam\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1 BUILD FAILED (total time: 0 seconds)

> The second error when try to define my_max_val: Exception in thread

Exception in thread "main" java.sql.SQLException: Before start of result set at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:959) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:862) at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:790) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2469) at com.mysql.jdbc.ResultSetImpl.getInt(ResultSetImpl.java:2580) at MyPackage.TestMax.main(TestMax.java:23) C:\Users\lam\AppData\Local\NetBeans\Cache\8.1\executor-snippets\run.xml:53: Java returned: 1 BUILD FAILED (total time: 0 seconds)

public static void main(String[] args) throws Exception {
        Connection myConn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database","user","pass");
        Statement myStmt = myConn.createStatement();
        ResultSet myRs = myStmt.executeQuery("SELECT MAX(ID) FROM table");
        int i = myRs.getInt("MAX(ID)")+1;
        System.out.println(i);
}

The second code

public static void main(String[] args) throws Exception {

    Connection myConn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database","user","pass");
    Statement myStmt = myConn.createStatement();
    ResultSet myRs = myStmt.executeQuery("SELECT MAX(ID) as my_max_val FROM table");
    int i = myRs.getInt("my_max_val")+1;
    System.out.println(i);

}

Answer 1

You have to define a name for the max value, so, that it will understand which output you want, as below, plus, move the iterator of the result set:

    Connection myConn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database","user","pass");
    Statement myStmt = myConn.createStatement();
    ResultSet myRs = myStmt.executeQuery("SELECT MAX(ID) as my_max_val FROM table");

    myRs.next(); //you might also have forgotten this
    int i = myRs.getInt("my_max_val")+1;
    System.out.println(i);

Answer 2

You do not have to define a name for max value if you simply use an columnIndex to retrieve the value

e.g.

 int i = myRs.getInt(1)+1;
 System.out.println(i);

columnIndex - the first column is 1, the second is 2, ...

http://docs.oracle.com/javase/7/docs/api/java/sql/ResultSet.html#getInt(int)

See also

ResultSet: Retrieving column values by index versus retrieving by label

for the benefit of retrieving by Label though.