>I need to write a query to find out a set of missing number in a given sequence.<<

Here is a classix version of this problem:

Let's assume we have a table of people who bought tickets that are

supposed to be in sequential order and we want to make a list of what

is missing in each buyer's set of tickets.

CREATE TABLE Tickets

(buyer CHAR(5) NOT NULL,

ticket_nbr INTEGER DEFAULT 1 NOT NULL

CHECK (ticket_nbr 0),

PRIMARY KEY (buyer, ticket_nbr));

INSERT INTO Tickets VALUES ('a', 2);

INSERT INTO Tickets VALUES ('a', 3);

INSERT INTO Tickets VALUES ('a', 4);

INSERT INTO Tickets VALUES ('b', 4);

INSERT INTO Tickets VALUES ('c', 1);

INSERT INTO Tickets VALUES ('c', 2);

INSERT INTO Tickets VALUES ('c', 3);

INSERT INTO Tickets VALUES ('c', 4);

INSERT INTO Tickets VALUES ('c', 5);

INSERT INTO Tickets VALUES ('d', 1);

INSERT INTO Tickets VALUES ('d', 6);

INSERT INTO Tickets VALUES ('d', 7);

INSERT INTO Tickets VALUES ('d', 9);

INSERT INTO Tickets VALUES ('e', 10);

If we can assume that there is a relatively small number of Tickets,

then you could use a table of sequential numbers from 1 to (n) and

write:

SELECT DISTINCT T1.buyer, S1.seq

FROM Tickets AS T1, Sequence AS S1

WHERE seq <= (SELECT MAX(ticket_nbr) -- set the range

FROM Tickets AS T2

WHERE T1.buyer = T2.buyer)

AND seq NOT IN (SELECT ticket_nbr -- get missing numbers

FROM Tickets AS T3

WHERE T1.buyer = T3.buyer);

Another version:

BEGIN

SELECT *

INTO #foobar

FROM Tickets

UNION ALL

SELECT DISTINCT buyer, 0

FROM Tickets;

SELECT T1.buyer,

(T1.ticket_nbr + 1) AS gap_start,

(MIN(T2.ticket_ nbr) - 1) AS gap_end

FROM --Tickets AS T1,

#foobar AS T1,

Tickets AS T2

WHERE T1.ticket_nbr < T2.ticket_nbr

AND T1.buyer = T2.buyer

GROUP BY T1.buyer, T1.ticket_nbr

HAVING MIN(T2.ticket_n br) - T1.ticket_nbr 1;

END;

The trick here is to add a zero to act as a boundary when 1 is missing

from the sequence.

In Standard SQL-92, you could write the UNION ALL expression directly

in the FROM clause.