MySql complex query - SUM on multiple and variable columns - mysql

Question

I have the following table structure (simplified version)
+----------------+ +-----------------+ +------+
| fee_definition | | user_fee | | user |
+----------------+ +-----------------+ +------+
| id | | user_id | | id |
| label | | fee_id | | ... |
| case1 | | case | +------+
| case2 | | manual_override |
| case3 | +-----------------+
| case4 |
| case5 |
+----------------+
Base on a pretty simple algorithm id determine which case fits the user to determine the amount of money they have to pay. A user_fee can be base on 1 to no limit number of fees definitions. which mean i can have the following content in the intersection table
+-----------+----------+--------+-------------------+
| user_id | fee_id | case | manual_override |
+-----------+----------+--------+-------------------+
| 1 | 1 | case1 | |
| 1 | 3 | case1 | |
| 1 | 5 | case1 | 50.22 |
| 2 | 1 | case5 | |
| 3 | 1 | case2 | |
| 3 | 2 | case2 | 18.50 |
+-----------+----------+--------+-------------------+
If a user is setted to have the case 1, all the fees listed under the case 1 where the value is different from 0 get picked. Same goes for the four other cases.
Just for reference on how i did things here is the actual query that I execute which is written in french (sorry for that but since we are a team of french speaking developpers, we mostly write in our code and queries in french).:
SELECT
`etudiant_etu`.*,
`session_etudiant_set`.*,
SUM(ROUND(frais_session_etudiant.fse_frais_manuel*100)/100) AS `fse_frais_manuel`,
`frais_session_etudiant`.`des_colonne`,
SUM(ROUND(definition_frais_des.des_quebecCanada*100)/100) AS `des_quebecCanada`,
SUM(ROUND(definition_frais_des.des_etranger*100)/100) AS `des_etranger`,
SUM(ROUND(definition_frais_des.des_non_credite*100)/100) AS `des_non_credite`,
SUM(ROUND(definition_frais_des.des_visiteur*100)/100) AS `des_visiteur`,
SUM(ROUND(definition_frais_des.des_explore*100)/100) AS `des_explore`,
`type_etudiant_tye`.*,
`type_formation_tyf`.*,
`pays_pys`.*,
`province_prc`.*
FROM `etudiant_etu`
INNER JOIN `session_etudiant_set`
ON session_etudiant_set.etu_id = etudiant_etu.etu_id
INNER JOIN `frais_session_etudiant`
ON frais_session_etudiant.set_id = session_etudiant_set.set_id
INNER JOIN `definition_frais_des`
ON definition_frais_des.des_id = frais_session_etudiant.des_id
LEFT JOIN `type_etudiant_tye`
ON type_etudiant_tye.tye_id = session_etudiant_set.tye_id
LEFT JOIN `type_formation_tyf`
ON type_formation_tyf.tyf_id = session_etudiant_set.tyf_id
LEFT JOIN `pays_pys`
ON pays_pys.pys_code = etudiant_etu.pys_adresse_permanente_code
LEFT JOIN `province_prc`
ON province_prc.prc_code = etudiant_etu.prc_adresse_permanente_code
WHERE (set_session = 'P11')
GROUP BY `session_etudiant_set`.`set_id`
ORDER BY `etu_nom` asc, `etu_prenom` ASC
as for reference from the actual query with the simplified version:
simplified version actual version
fee_definition.id definition_frais_des.des_id
fee_definition.case1 definition_frais_des.des_quebecCanada
fee_definition.case2 definition_frais_des.des_etranger
fee_definition.case3 definition_frais_des.des_non_credite
fee_definition.case4 definition_frais_des.des_visiteur
fee_definition.case5 definition_frais_des.des_explore
user_fee.user_id frais_session_etudiant.set_id
user_fee.fee_id frais_session_etudiant.des_id
user_fee.case frais_session_etudiant.des_colonne
user_fee.manual_override frais_session_etudiant.fes_frais_manuel
user.id session_etudiant_set.set_id
The problem I have is when it comes to handling the manual override setting. What would be the best way of doing this?
I would rather this to be handled in the query itself than in the programmation.
the logic behind what I am looking for goes as follow
get the SUM of the fees to be charged for a user and if an override value as been set, use that value instead of the actual value setted in the fee_definition, else use the value in the fee_definition.
I don't mind to loose the 4 not used cases and only keep the right column
Edited to display final result
This is the query I ended with, five levels of IF's
'IF(`frais_session_etudiant`.des_colonne= "des_quebec_canada",
SUM(IF(`frais_session_etudiant`.fse_frais_manuel > 0,
ROUND(`frais_session_etudiant`.fse_frais_manuel*100)/100,
ROUND(definition_frais_des.des_quebec_canada*100)/100)
),
IF(`frais_session_etudiant`.des_colonne= "des_etranger",
SUM(IF(`frais_session_etudiant`.fse_frais_manuel > 0,
ROUND(`frais_session_etudiant`.fse_frais_manuel*100)/100,
ROUND(definition_frais_des.des_etranger*100)/100)
),
IF(`frais_session_etudiant`.des_colonne= "des_non_credite",
SUM(IF(`frais_session_etudiant`.fse_frais_manuel > 0,
ROUND(`frais_session_etudiant`.fse_frais_manuel*100)/100,
ROUND(definition_frais_des.des_non_credite*100)/100)
),
IF(`frais_session_etudiant`.des_colonne= "des_visiteur",
SUM(IF(`frais_session_etudiant`.fse_frais_manuel > 0,
ROUND(`frais_session_etudiant`.fse_frais_manuel*100)/100,
ROUND(definition_frais_des.des_visiteur*100)/100)
),
IF(`frais_session_etudiant`.des_colonne= "des_explore",
SUM(IF(`frais_session_etudiant`.fse_frais_manuel > 0,
ROUND(`frais_session_etudiant`.fse_frais_manuel*100)/100,
ROUND(definition_frais_des.des_explore*100)/100)
),
0
)
)
)
)
) as frais'
That's a monster! as said by Ted Hopp :D

Answer 1

You can use IFNULL(manual_override,non-override-value)