Complicated MySql Update Join Query - mysql

Question

Have is an example of the problem I'm facing. The database tables are a little different than usual, but needed to be setup this way.
Items: id, order_id, other fields
Items_Drinks: id, drinks, other fields
Orders: id, other fields
Orders_Drinks: id, drinks, other fields
I need to have an update query that will update the Orders_Drinks table with the sum of the Items_Drinks drinks field that have the same order_id as Orders_Drinks id field.
Items: 1 1 ...
Items: 2 1 ...
Items_Drinks: 1 4 ...
Items_Drinks: 2 5 ...
Orders: 1 ...
Orders_Drinks: 1 9 ...
The Orders_Drinks is currently correct, but if I were to update Items_Drinks with id of 1 to 5, I would need an update command to get Orders_Drinks with id 1 to equal 10.
It would be best if the command would update every record of the Orders_Drinks.
I know my database is not typical, but it is needed for my application. This is because the Drinks table is not needed for all entries. The Drinks table has over 5000 fields in it, so if every record had these details the database would grow and slow for no real reason. Please do not tell me to restructure the database, this is needed.
I am currently using for loops in my C# program to do what I need, but having 1 command would save a ton of time!
Here is my best attempt, but it gives an error of "invalid group function".
update Orders_Drinks join Items on Items.order_id=Orders_Drinks.id join Items_Drinks on Items_Drinks.id=Items.id set Orders_Drinks.drinks=sum(Item_Drinks.drinks);

Answer 1

I think this is what you're wanting.
Edited:
UPDATE `Order_Drinks` a
SET a.`drinks` = (SELECT SUM(b.`drinks`) FROM `Items_Drinks` b INNER JOIN `Items` c ON (b.`id` = c.`id`) WHERE a.`id` = c.`order_id`)
That should give you a total of 9 for the Order_Drinks table for the row id of 1.
This is assuming that Orders.id == Orders_Drinks.id and that Items.id == Items_Drinks.id.

Answer 2

You need to do an aggregation. You can do this in the join part of the update statement:
update Orders_Drinks od join
(select i.order_id, sum(id.drinks) as sumdrinks
from Items i join
Items_Drinks id
on id.id = i.id
) iid
on iid.order_id = od.id
set od.drinks = iid.sumdrinks;

Answer 3

Something like this will return the id from the orders_drinks table, along with the current value of the drinks summary field, and a new summary value derived from the related items_drinks tables.
(Absent the name of the foreign key column, I've assumed the foreign key column names are of the pattern: "referenced_table_id" )
SELECT od.id
, od.drinks AS old_drinks
, IFNULL(td.tot_drinks,0) AS new_drinks
FROM orders_drinks od
LEFT
JOIN ( SELECT di.orders_drinks_id
, SUM(di.drinks) AS tot_drinks
FROM items_drinks di
GROUP BY di.orders_drinks_id
) td
ON td.orders_drinks_id = od.id
Once we have SELECT query written that gets the result we want, we can change it into an UPDATE statement. Just replace SELECT ... FROM with the UPDATE keyword, and add a SET clause, to assign/replace the value to the drinks column.
e.g.
UPDATE orders_drinks od
LEFT
JOIN ( SELECT di.orders_drinks_id
, SUM(di.drinks) AS tot_drinks
FROM items_drinks di
GROUP BY di.orders_drinks_id
) td
ON td.orders_drinks_id = od.id
SET od.drinks = IFNULL(td.tot_drinks,0)
(NOTE: the IFNULL function is optional. I just used it to substitute a value of zero whenever there are no matching rows in items_drinks found, or whenever the total is NULL.)
This will update all rows (that need to be updated) in the orders_drinks table. A WHERE clause could be added (after the SET clause), if you only wanted to update particular rows in orders_drinks, rather than all rows:
WHERE od.id = 1
Again, to get to this, first get a SELECT statement working to return the new value to be assigned to the column, along with the key of the table to be updated. Once that is working, convert it into an UPDATE statement, moving the expression that returns the new value down to a SET clause.