HSQL Trigger generates SQL Error: -458, SQLState: S1000 / java.lang.ArrayIndexOutOfBoundsException - triggers

Question

I have an HSQL version of an Oracle database schema to perform unit tests.
I need to update a column on update with current timestamp.
The trigger I have implemented is loaded without complaint by the hsql engine, but it crashes at runtime when I try to update rows.
Here is a sample test case that you can run in a project configured with spring and junit:
public class UtSqlTriggerTest {
#Test public void testTrigger() throws SQLException {
ResourceDatabasePopulator resourceDatabasePopulator = new ResourceDatabasePopulator();
resourceDatabasePopulator.addScript(new InMemoryResource(
"CREATE TABLE TEST (ID NUMERIC NOT NULL PRIMARY KEY,DATA VARCHAR(200), LAST_UPDATE TIMESTAMP);\n" +
"CREATE TRIGGER updTimestamp AFTER UPDATE OF DATA ON TEST\n" +
"REFERENCING NEW AS newrow OLD AS oldrow\n" +
"FOR EACH ROW\n" +
"SET newrow.LAST_UPDATE = current_timestamp;"));
Connection connection = DriverManager.getConnection("jdbc:hsqldb:file:/opt/db/testdb;shutdown=true", "SA", "");
resourceDatabasePopulator.populate(connection);
JdbcTemplate tjdbc = new JdbcTemplate(new SingleConnectionDataSource(connection, true));
tjdbc.update("INSERT INTO TEST(ID, DATA) VALUES (0, 'HELLO')");
tjdbc.update("UPDATE TEST SET DATA = 'HELLO WORLD' WHERE ID = 0");
tjdbc.queryForObject("SELECT LAST_UPDATE FROM TEST WHERE ID = 0", Date.class);
}
}
What's wrong with this trigger ? Why it generated ArrayIndexOutOfBoundException ?
CREATE TRIGGER updateDateAjoutFichier AFTER UPDATE OF DATA ON TEST
REFERENCING NEW AS newrow OLD AS oldrow
FOR EACH ROW
SET newrow.LAST_UPDATE = current_timestamp;

Answer 1

When you run the CREATE TRIGGER in a SQL client you will see the following error message:
attempt to assign to non-updatable column: LAST_UPDATE [SQL State=0U000, DB Errorcode=-2500]
This is because you are trying to modify a column in an AFTER trigger. Changing column values is only possible in a BEFORE trigger. So you should use:
CREATE TRIGGER updTimestamp BEFORE UPDATE OF DATA ON TEST
REFERENCING NEW AS newrow OLD AS oldrow
FOR EACH ROW
SET newrow.LAST_UPDATE = current_timestamp;