Question

I have a table that looks like

id
Type: Auto inc-int
Comment: the unique id
Value Inserted auto inc int

dateGained
Type: dateTime
Comment: Date currency was gained
Value inserted: Current Date/Time

amntGained
Type: float
Comment: Amount of currency gained
Value inserted: value gained (e.g. 0.25)

amntUsed
Type: float
Comment: When part of the value is used this column gets updated
Value inserted: 0

uuid
Type: uuid
Comment: The users uuid
Value inserted: (a uuid)

so a few example rows (for a single user) would be

1 | 2010-07-30 00:00:00 | 0.25 | 0.20 | [uuid]  
2 | 2010-08-12 00:00:00 | 1.75 | 0.00 | [uuid]  
3 | 2010-08-17 00:00:00 | 8.25 | 0.00 | [uuid]  
4 | 2010-09-15 00:00:00 | 0.05 | 0.00 | [uuid]  

Now my question is around the logic:

Basically I have a function that is given a uuid and an amount, the function then has to go through starting from the oldest and update the used value untill the amount given is satisfied.

e.g. if the function was given 6.25 and [uuid]

The table would look like

1 | 2010-07-30 00:00:00 | 0.25 | 0.25 | [uuid] //still need to use 6.20  
2 | 2010-08-12 00:00:00 | 1.75 | 1.75 | [uuid] //still need to use 4.45 
3 | 2010-08-17 00:00:00 | 8.25 | 4.45 | [uuid] //we now have 3.80 remaining 
4 | 2010-09-15 00:00:00 | 0.05 | 0.00 | [uuid] //this row is untouched 

but I have a complete mind blank on how to do this efficiently or at all for that matter.

Answer 1

Will it work for you? (Updated version)

UPDATE table1 t3
INNER JOIN
(
SELECT t1.id, IFNULL(SUM(t2.amntGained),0) as total // 0 for the smallest date
FROM table1 t1
LEFT JOIN table1 t2 ON (t2.uuid = t1.uuid AND t2.dateGained < t1.dateGained)
// LEFT JOIN,not INNER because "<" is used for joining, 
WHERE uuid = 1
GROUP BY t1.id
)X  ON (X.id=t3.id)
SET t3.amntUsed = IF(X.total+t3.amntGained <=6.25, t3.amntGained, 
 IF(6.25-X.total>0, 6.25-X.total,0))
WHERE t3.uuid=1

For your data:

id - total - amntGained - X.total+t3.amntGained - 6.25-X.total>0 - new.amntUsed
1  - 0     - 0.25      - 0.25                   - true             0.25
2  - 0.25  - 1.75      - 2                      - true             1.75
3  - 2     - 8.25      - 10.25                  - true             6.25-2 = 4.25
4  - 10.25 - 0.05      - 10.30                  - false            0