Creating a third alias from the remainder of two aliases in MYSQL? - mysql

Question

Is it possible to create a third alias from the remainder of two aliases in MYSQL?
Here is my query:
SELECT DISTINCT
workcards.task,
workcards.program,
workcards.zone,
workcards.CYLcomp,
workcards.CYLint,
workcards.task,
workcards.CYLcomp + workcards.CYLint AS nextdue,
workcards.wcnumber,
(SELECT airtimes.total_cycles
FROM airtimes
WHERE airtimes.nnumber='xxxxx'
ORDER BY airtimes.total_cycles DESC LIMIT 1) AS current_cycle
FROM workcards
WHERE basis LIKE '%CYL%'
AND nnumber='xxxxx'
ORDER BY CASE nextdue
WHEN 0 THEN 1 ELSE -1 END ASC, nextdue ASC
What I want to do is create a third alias which would be the difference of the 'nextdue' minus 'current_cyle' aliases? Something like:
nextdue - current_cycle AS remainder?
Sorry if noob or whatever.
Thanks

Answer 1

You cannot use calculations results aliases to use with another calculations in select part (http://dev.mysql.com/doc/refman/5.0/en/problems-with-alias.html). But you can get what you want by rebuilding your query so it will use joins and grouping:
SELECT DISTINCT
w.*,
w.CYLcomp + w.CYLint AS nextdue,
MAX(a.total_cycles) AS current_cycle
w.CYLcomp + w.CYLint - MAX(a.total_cycles) AS reminder
FROM workcards w
JOIN airtimes a ON a.nnumber = w.nnumber
WHERE w.basis LIKE '%CYL%' AND w.nnumber='xxxxx'
GROUP BY w.nnumber
ORDER BY CASE nextdue WHEN 0 THEN 1 ELSE -1 END ASC, nextdue ASC