This section describes what will happen if you try to insert rows with values for GENERATED ALWAYS AS IDENTITY columns.
An INDENTITY column is a special column in a table that is defined to have its values automatically added with
a sequence number generator. An INDENTITY column is normally used for the primary key column in a table.
For example, the ID column in the Profile table created in a previous tutorial is an INDENTITY column.
If an IDENTITY column is defined with "GENERATED ALWAYS AS IDENTITY" and you try to add values to this column in INSERT statements,
you will get an error as shown in the sample program below:
/**
* DerbyInsertIdentity.java
* Copyright (c) 2007 by Dr. Herong Yang. All rights reserved.
*/
import java.sql.*;
public class DerbyInsertIdentity {
public static void main(String [] args) {
Connection con = null;
try {
con = DriverManager.getConnection(
"jdbc:derby://localhost/TestDB");
Statement sta = con.createStatement();
// insert a single row
int count = sta.executeUpdate(
"INSERT INTO Profile"
+ " (ID, FirstName, LastName, ModTime)"
+ " VALUES (1001, 'Herong', 'Yang', '2007-04-01')");
System.out.println("Number of rows inserted: "+count);
sta.close();
con.close();
} catch (Exception e) {
System.err.println("Exception: "+e.getMessage());
}
}
}
Here is the error message from this program:
Exception: Attempt to modify an identity column 'ID'.
