Welcome to WebmasterWorld Guest from 23.20.5.37

Forum Moderators: open

Message Too Old, No Replies

MySQL query with a variable which results randomly change

Problem with a particular query

     
11:33 am on Nov 14, 2011 (gmt 0)

5+ Year Member



Hello,

I have a query that seems it changes its result randomly. I supose that I'm doing something wrong but when I review my query I don't find it. I hope you could help me.

The query orders the results and I use a variable for getting the row position:

SET @row_number_old :=0;
SELECT p.id, p.name, f.id, f.others, s.value, s.old_value, (
@row_number_old := @row_number_old +1
) AS old_position
FROM profile p
INNER JOIN other_table f ON f.profile_id = p.id
INNER JOIN score s ON s.profile_id = p.id
WHERE 1
ORDER BY old_value DESC


Despite the data stored in the DB is always the same, the problem is that 'old_position' value is not always the same in the results. Sometimes it has the correct value (the row position), but another times it has the value of f.id inexplicably.
7:29 pm on Jan 2, 2012 (gmt 0)

WebmasterWorld Administrator coopster is a WebmasterWorld Top Contributor of All Time 10+ Year Member



Is it because of your ORDER BY? It seems that could be the issue. Also, although you may be OK in this query, for future reference you may want to be careful reading and setting in the same SELECT query:

While it is also possible both to set and to read the value of the same variable in a single SQL statement using the := operator, this is not recommended. Section 8.4, “User-Defined Variables”, explains why you should avoid doing this.


[dev.mysql.com...]
[dev.mysql.com...]
 

Featured Threads

Hot Threads This Week

Hot Threads This Month