DB2 SQL Triggers - sql

Question

I'm pretty new (like read-about-it-5-hours-ago-new) into Triggers, so I need some help on this:
Create the table TelefonnummerAenderung and delete all data in it if it already exists.
Create a Trigger meeting the following conditions: (I hope it's ok for you guys if I don't translate all the table names and attributes into English.)
-a change of the attribute Telefonnummer in KundenKontaktDaten is only allowed 15 secs after the last change
-otherwise a SIGNAL SQLSTATE '70001' is thrown
-while changing the Telefonnummer in KundenKontaktDaten a new entry in TelefonnummerAenderungen is created containing the old Telefonnummer and the time it was changed
-if the new and the old Telefonnummer are the same, no trigger action takes place
The two tables are the following:
KundenKontaktDaten: (edit: I forgot, Kunden_Nr is also referencing Kunde(Kunden_Nr). It should not matter for the task, just saying)
create table KundenKontaktDaten
( Kunden_Nr int not null primary key,
Twitter_Id Varchar(40),
Google_Id bigint,
Facebook_Id bigint,
Skype_Id Varchar(64),
Telefonnummer Varchar(50)
);
TelefonnummerAenderungen:
create table TelefonnummerAenderungen
( GEAENDERT_AM TIMESTAMP NOT NULL,
KUNDEN_NR INTEGER NOT NULL,
ALTE_NUMMER VARCHAR(50),
FOREIGN KEY(KUNDEN_NR)
REFERENCES KUNDE(KUNDEN_NR)
ON DELETE CASCADE
ON UPDATE RESTRICT,
PRIMARY KEY(GEAENDERT_AM, KUNDEN_NR)
);
My solution(java code; should not matter concerning the question):
static public void triggerAnlegen(Connection con) throws SQLException {
Statement stmt = con.createStatement();
try {
stmt.execute("create table TelefonnummerAenderungen ( GEAENDERT_AM TIMESTAMP NOT NULL, KUNDEN_NR INTEGER NOT NULL, ALTE_NUMMER VARCHAR(50), FOREIGN KEY(KUNDEN_NR) REFERENCES KUNDE(KUNDEN_NR) ON DELETE CASCADE ON UPDATE RESTRICT, PRIMARY KEY(GEAENDERT_AM, KUNDEN_NR))");
} catch (SQLException e) {
if(e.getErrorCode()==-601){
stmt.execute("DELETE FROM TelefonnummerAenderungen");
}
}
try{
stmt.execute("CREATE TRIGGER haTrigger AFTER UPDATE OF Telefonnummer ON KundenKontaktDaten REFERENCING NEW as n_row OLD as o_row FOR EACH ROW WHEN (o_row.Telefonnummer<>n_row.Telefonnummer) "+
"BEGIN " +
"IF(NOT EXISTS(SELECT * FROM TelefonnummerAenderungen WHERE Kunden_Nr=n_row.Kunden_Nr)) " +
"THEN " +
"INSERT INTO TelefonnummerAenderungen VALUES (CURRENT TIMESTAMP,n_row.Kunden_Nr,o_row.Telefonnummer); " +
"ELSEIF(CURRENT TIMESTAMP<((SELECT GEAENDERT_AM FROM TelefonnummerAenderungen WHERE Kunden_Nr=n_row.Kunden_Nr) + 15 seconds)) " +
"THEN " +
"UPDATE KundenKontaktDaten SET Kunden_Nr=o_row.Kunden_Nr,Twitter_Id=o_row.Twitter_Id,Google_Id=o_row.Google_Id,Facebook_Id=o_row.Facebook_Id,Skype_Id=o_row.Skype_Id,Telefonnummer=o_row.Telefonnummer;" +
"SIGNAL SQLSTATE '70001'; " +
"ELSE " +
"UPDATE TelefonnummerAenderungen SET GEAENDERT_AM=CURRENT TIMESTAMP,ALTE_NUMMER=o_row.Telefonnummer WHERE Kunden_Nr=n_row.Kunden_Nr; " +
"END IF;" +
"END");
} catch (SQLException e) {
throw e;
}
}
SQL-only:
CREATE TRIGGER haTrigger
AFTER UPDATE OF Telefonnummer ON KundenKontaktDaten
REFERENCING
NEW as n_row
OLD as o_row
FOR EACH ROW WHEN (o_row.Telefonnummer <> n_row.Telefonnummer)
BEGIN
IF (NOT EXISTS (SELECT *
FROM TelefonnummerAenderungen
WHERE Kunden_Nr=n_row.Kunden_Nr)
)
THEN
INSERT INTO TelefonnummerAenderungen
VALUES
(CURRENT TIMESTAMP, n_row.Kunden_Nr, o_row.Telefonnummer);
ELSEIF (CURRENT TIMESTAMP < ((SELECT GEAENDERT_AM
FROM TelefonnummerAenderungen
WHERE Kunden_Nr=n_row.Kunden_Nr) + 15 seconds)
)
THEN
UPDATE KundenKontaktDaten
SET Kunden_Nr = o_row.Kunden_Nr,
Twitter_Id = o_row.Twitter_Id,
Google_Id = o_row.Google_Id,
Facebook_Id = o_row.Facebook_Id,
Skype_Id = o_row.Skype_Id,
Telefonnummer = o_row.Telefonnummer;
SIGNAL SQLSTATE '70001';
ELSE
UPDATE TelefonnummerAenderungen
SET GEAENDERT_AM = CURRENT TIMESTAMP,
ALTE_NUMMER = o_row.Telefonnummer
WHERE Kunden_Nr = n_row.Kunden_Nr;
END IF;
END
I used the AFTER UPDATE OF [...] because I was not sure, whether (when using BEFORE UPDATE OF [...]) the query, which caused the trigger to trigger, is still being executed after the trigger handling .
[edit: changed it to BEFORE and dropped the
UPDATE KundenKontaktDaten
SET Kunden_Nr = o_row.Kunden_Nr,
Twitter_Id = o_row.Twitter_Id,
Google_Id = o_row.Google_Id,
Facebook_Id = o_row.Facebook_Id,
Skype_Id = o_row.Skype_Id,
Telefonnummer = o_row.Telefonnummer;
because I was getting cascading trigger errors otherwise ; won't change the code here though for matter of transparency]
This is (obviously) my homework (no real-world-problem, hope that's ok, and we get graded automatically by some test function we don't know - that way I know my results are wrong.
But I don't know which part of it is wrong, so I need some help on this.
Edit 2:
My post is getting kind of confusing, sorry. I thought creating an answer would be more clear than further editing of my post:
After further testing I figured out the problem with the first attempt:
When using 'AFTER UPDATE...' in my trigger, it's too late and I can't undo the changes made to 'KundenKontaktDaten' although the 15 seconds didn't pass, since it would result in cascading trigger calls.
When using 'BEFORE UPDATE...' DB2 restricts me of using any kind of INSERT or UPDATE.
So I figured out I have to use INSTEAD OF:
CREATE TRIGGER haTrigger INSTEAD OF UPDATE ON KundenKontaktDaten REFERENCING NEW as n_row OLD as o_row FOR EACH ROW
BEGIN
IF(o_row.Telefonnummer<>n_row.Telefonnummer) THEN
IF(NOT EXISTS(SELECT * FROM TelefonnummerAenderungen WHERE Kunden_Nr=n_row.Kunden_Nr)) THEN
UPDATE KundenKontaktDaten SET Kunden_Nr=n_row.Kunden_Nr,Twitter_Id=n_row.Twitter_Id,Google_Id=n_row.Google_Id,Facebook_Id=n_row.Facebook_Id,
Skype_Id=n_row.Skype_Id,Telefonnummer=n_row.Telefonnummer WHERE Kunden_Nr=o_row.Kunden_Nr;
INSERT INTO TelefonnummerAenderungen VALUES (CURRENT TIMESTAMP,n_row.Kunden_Nr,o_row.Telefonnummer);
ELSEIF(CURRENT TIMESTAMP<((SELECT GEAENDERT_AM FROM TelefonnummerAenderungen WHERE Kunden_Nr=n_row.Kunden_Nr) + 15 seconds)) THEN
SIGNAL SQLSTATE '70001';
ELSE
UPDATE KundenKontaktDaten SET Kunden_Nr=n_row.Kunden_Nr,Twitter_Id=n_row.Twitter_Id,Google_Id=n_row.Google_Id,Facebook_Id=n_row.Facebook_Id,
Skype_Id=n_row.Skype_Id,Telefonnummer=n_row.Telefonnummer WHERE Kunden_Nr=o_row.Kunden_Nr;
UPDATE TelefonnummerAenderungen SET GEAENDERT_AM=CURRENT TIMESTAMP,ALTE_NUMMER=o_row.Telefonnummer WHERE Kunden_Nr=n_row.Kunden_Nr;
END IF;
END IF;
END
resulting in yet another error:
DB2 SQL Error: SQLCODE=-159, SQLSTATE=42809,
SQLERRMC=GRP13.KUNDENKONTAKTDATEN;TABLE;UNTYPED VIEW
Since I have no idea, does anyone know what's the problem with that one? If neither Before nor After nor Instead of works, then I'm kind of running out of options.

Answer 1

I don't think you need to include the UPDATE of KundenKontaktDaten in the trigger, because the table is already modified by the statement that invokes the trigger. It probably should look somewhat like this:
CREATE TRIGGER haTrigger
AFTER UPDATE OF Telefonnummer ON KundenKontaktDaten
REFERENCING NEW as n_row OLD as o_row
FOR EACH ROW
WHEN (o_row.Telefonnummer<>n_row.Telefonnummer)
BEGIN
IF EXISTS (
SELECT 1 FROM TelefonnummerAenderungen a
WHERE a.Kunden_Nr = o_row.Kunden_Nr
AND a.GEAENDERT_AM > CURRENT TIMESTAMP - 15 seconds
)
THEN -- within the 15 sec. window, record old telephone number
INSERT INTO TelefonnummerAenderungen
VALUES (CURRENT TIMESTAMP, o_row.Kunden_Nr,o_row.Telefonnummer);
ELSE -- too late
SIGNAL SQLSTATE '70001';
END IF;
END
PS. Not tested.
PPS. You probably should store GEAENDERT_AM also in KundenKontaktDaten to avoid the extra query.