MySQL - Insert multiple rows based on column value - mysql

Question

I have the query working, just wondering if there is a better way to do this without cursors/loops/php side. I've been a DBA for 5+ years and just came across the := statement. Very cool.
Table (tblPeople) with the person ID and the number of tickets they bought.
PersonId NumTickets
1 3
2 1
3 1
I then want to assign individual tickets to each person in a new table (tblTickets), depending on how many tickets they bought. The TicketId is a key, auto increment column.
TicketId PersonId
100 1
101 1
102 1
103 2
104 3
Here is the code. It loops through the whole tblPeople over and over again incrementing a new calculated column called rowID. Then I filter out the rows based on the number of tickets they bought in the WHERE clause. The problem I see is the subquery is huge, the more people I have, the bigger the subquery gets. Just not sure if there is a better way to write this.
INSERT INTO tblTickets (PersonId)
SELECT PersonId
FROM (
SELECT s.PersonId, s.NumTickets,
#rowID := IF(#lastPersonId = s.PersonId and #lastNumTickets = s.NumTickets, #rowID + 1, 0) AS rowID,
#lastPersonId := s.PersonId,
#lastNumTickets := s.NumTickets
FROM tblPeople m,
(SELECT #rowID := 0, #lastPersonId := 0, #lastNumTickets := 0) t
INNER JOIN tblPeople s
) tbl
WHERE rowID < NumTickets

Answer 1

I'd add a utility table Numbers which contains all the numbers from 1 up to the maximal number of tickets a person may buy. Then you can do something like this:
INSERT INTO tblTickets (PersonId)
SELECT s.PersonId
FROM tblPeople s, Numbers n
WHERE n.number <= s.NumTickets

Answer 2

Following Stored procedure will serve your purpose...
DELIMITER $$
USE <your database name> $$
DROP PROCEDURE IF EXISTS `update_ticket_value2`$$
CREATE PROCEDURE `update_ticket_value2`()
BEGIN
DECLARE index_value INT;
DECLARE loop_variable INT;
SET #KeyValue = 100;
SET #LastPersonID = 0;
SET #TicketNum = 0;
SET #PersonIDToHandle = 0;
SELECT #PersonIDToHandle = PersonID, #TicketNum = NumTickets
FROM tblPeople
WHERE PersonId > #LastPersonID
ORDER BY PersonId
LIMIT 0,1;
WHILE #PersonIDToHandle IS NOT NULL
DO
SET loop_variable = 0;
WHILE(loop_variable < #TicketNum) DO
INSERT INTO tblTickets(TicketId, PersonId) VALUES(#KeyValue + loop_variable, #PersonIDToHandle);
SET loop_variable = loop_variable + 1;
END WHILE;
SET #LastPersonID = #PersonIDToHandle;
SET #PersonIDToHandle = NULL;
SET #KeyValue = #KeyValue + #TicketNum;
SELECT #PersonIDToHandle := PersonID, #TicketNum := NumTickets
FROM tblPeople
WHERE PersonId > #LastPersonID
ORDER BY PersonId
LIMIT 0,1;
END WHILE;
END$$
DELIMITER ;
Call the procedure as:
CALL update_ticket_value2();
Hope it helps...