Hi all,

I have a master (X) and a detail (Y) table. Table X contains a
timestamp and the sum of the amounts of its details. Table Y
on the other hand, contains detail information such as description,
quantity, unit price, amount and the ISRETURNED column, which
indicates whether this item is returned (1) or not (0). All amounts
are positive values.

Now, the AMOUNT fiels of table X is computed by subtracting all
detail records where ISRETURNED = 1 from detail records having
ISRETURNED = 0.

Using the script at the end of this message, I executed the ff. query:

SELECT * FROM X;

and yielded...

1/1/2003 3323.75
2/1/2003 1441.75
3/1/2003 379

...which is correct. But when I queried the SUM() of the AMOUNT
column:

SELECT SUM(AMOUNT) FROM X;

I get 9971.25 instead of 5144.5.

I found out that computed fields with normal SUM() selects are OK,
only selects like the AMOUNT column in table X.

Anything wrong with my script?

Thanks :)

SQL script follows:

CREATE TABLE X
(
DATETIME TIMESTAMP NOT NULL,
PRIMARY KEY (DATETIME)
);

CREATE TABLE Y
(
DATETIME TIMESTAMP NOT NULL,
DESCRIPTION VARCHAR(20) NOT NULL,
QUANTITY INTEGER NOT NULL,
UNITPRICE NUMERIC(15, 2) NOT NULL,
AMOUNT COMPUTED BY (QUANTITY * UNITPRICE),
ISRETURNED SMALLINT DEFAULT 0 NOT NULL,
PRIMARY KEY (DATETIME, DESCRIPTION)
);

ALTER TABLE Y
ADD CONSTRAINT Y_X
FOREIGN KEY (DATETIME)
REFERENCES X (DATETIME)
ON UPDATE CASCADE
ON DELETE CASCADE;

ALTER TABLE X
ADD AMOUNT COMPUTED BY
((SELECT (SELECT COALESCE(SUM(AMOUNT), 0)
FROM Y
WHERE DATETIME = X.DATETIME AND
ISRETURNED = 0) -
(SELECT COALESCE(SUM(AMOUNT), 0)
FROM Y
WHERE DATETIME = X.DATETIME AND
ISRETURNED <> 0)
FROM RDB$DATABASE));

INSERT INTO X (DATETIME) VALUES ('1/1/2003');
INSERT INTO X (DATETIME) VALUES ('2/1/2003');
INSERT INTO X (DATETIME) VALUES ('3/1/2003');

INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('1/1/2003', 'PANTS', 5, 564.75, 0);
INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('1/1/2003', 'T-SHIRT', 2, 250.00, 0);

INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('2/1/2003', 'BLOUSE', 1, 290.25, 1);
INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('2/1/2003', 'SOCKS', 12, 123.5, 0);
INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('2/1/2003', 'T-SHIRT', 1, 250, 0);

INSERT INTO Y (DATETIME, DESCRIPTION, QUANTITY, UNITPRICE, ISRETURNED)
VALUES ('3/1/2003', 'POLO', 2, 189.5, 0);