SQLite: Update one column based on a condition set in another table - sql

Question

I'm a total noob in SQL and I've only just begun working with SQLite, and this is my first post here, so please pardon my inherent lack of understanding. I've been self-teaching myself after graduating with a BA, so please bear with me lol.
I've managed to get the following query to work, but only if all of the data was a part of the same table. I've since broken my two tables into three separate tables: widgetCustomer, widgetSale, and widgetOrderInfo.
UPDATE widgetOrderInfo
SET extendedcost = (cost * qty) * (0.80)
WHERE widgetCustomer.IsASenior = 'Y';
-- Seniors get a 20 percent discount;
^^ This is the part I'm having trouble with. Whenever I use this query SQLite returns, "No such column: IsASenior."
--NOTE: IsASenior is a column in widgetCustomer set to either 'Y' or 'N' based on a trigger earlier on in the code. I've gotten base multiplication to work very easily using only the data in the widgetOrderInfo table using the following query:
UPDATE widgetOrderInfo
SET extendedcost = (cost * qty);
Very basic, I'm aware, but I'm unsure what I must do in order to get my widgetOrderInfo table to acknowledge the data in widgetCustomer's 'IsASenior' column.
Do I have to use a JOIN in order to access data between two tables in an UPDATE statement?
Any assistance would be great! Thanks!
FULL LIST AND ORDER OF QUERIES I'M CURRENTLY PERFORMING (Lots of place-holders; WIP)
CREATE TABLE widgetCustomer
( id INTEGER PRIMARY KEY, name TEXT, age INT, IsASenior TEXT, last_order_id INT, soItemID INT );
CREATE TABLE widgetSale
( id INTEGER PRIMARY KEY, item_id INT, item_name TEXT, customer_id INT, quan INT, price MONEY(8,2) );
CREATE TABLE widgetOrderInfo
( id INTEGER PRIMARY KEY, salesOrderID INT, cost MONEY(8,2), qty INT, extendedcost MONEY(8,2) )
;
CREATE TRIGGER SeniorCheck AFTER INSERT ON widgetCustomer
BEGIN
UPDATE widgetCustomer
SET IsASenior = 'Y' WHERE age >= 65;
UPDATE widgetCustomer
SET IsASenior = 'N' WHERE age < 65;
END
;
INSERT INTO widgetCustomer (name, age, soItemID)
VALUES ('Ian', 24, 3);
INSERT INTO widgetCustomer (name, age, soItemID)
VALUES ('Andrew', 29, 2);
INSERT INTO widgetCustomer (name, age, soItemID)
VALUES ('John', 65, 1);
INSERT INTO widgetCustomer (name, age, soItemID)
VALUES ('Kathy', 60, 4)
;
CREATE TRIGGER newWidgetSale AFTER INSERT ON widgetSale
BEGIN
UPDATE widgetCustomer
SET last_order_id = NEW.id
WHERE widgetCustomer.id = NEW.customer_id;
END
;
INSERT INTO widgetSale (item_id, item_name, customer_id, quan, price)
VALUES (1, 'Blue Brick', 3, 50, 9.95);
INSERT INTO widgetSale (item_id, item_name, customer_id, quan, price)
VALUES (2, 'Red Brick', 2, 30, 4.95);
INSERT INTO widgetSale (item_id, item_name, customer_id, quan, price)
VALUES (3, 'Black Brick', 1, 24, 9.95);
INSERT INTO widgetSale (item_id, item_name, customer_id, quan, price)
VALUES (4, 'Yellow Brick', 4, 30, 9.95)
;
CREATE TRIGGER SubtractQuan AFTER INSERT ON widgetOrderInfo FOR EACH ROW
BEGIN
UPDATE widgetSale
SET quan = (quan - New.qty)
WHERE customer_id = New.id;
END
;
INSERT INTO widgetOrderInfo (salesOrderID, cost, qty)
VALUES (283001, 9.95, 4);
INSERT INTO widgetOrderInfo (salesOrderID, cost, qty)
VALUES (283002, 4.95, 8);
INSERT INTO widgetOrderInfo (salesOrderID, cost, qty)
VALUES (283003, 9.95, 5);
INSERT INTO widgetOrderInfo (salesOrderID, cost, qty)
VALUES (283004, 9.95, 15)
;
UPDATE widgetOrderInfo
SET extendedcost = (cost * qty)
;
SELECT
CASE
WHEN qty BETWEEN 5 and 7 THEN 'parcel'
WHEN qty BETWEEN 8 and 14 THEN 'package'
WHEN qty BETWEEN 15 and 30 THEN 'box'
WHEN qty BETWEEN 31 and 99 THEN 'crate'
ELSE 'individually wrapped'
END
AS PackagingBasedOnPurchaseSize,
COUNT(*) qty FROM widgetOrderInfo
GROUP BY
CASE
WHEN qty BETWEEN 5 and 7 THEN 'parcel'
WHEN qty BETWEEN 8 and 14 THEN 'package'
WHEN qty BETWEEN 15 and 30 THEN 'box'
WHEN qty BETWEEN 31 and 99 THEN 'crate'
ELSE 'individually wrapped'
END
;
SELECT * FROM widgetSale;
SELECT * FROM widgetCustomer;
SELECT * FROM widgetOrderInfo;
I can provide a link to my whole database if need be.

Answer 1

In an UPDATE statement, you can directly access only the updated table itself.
To access other tables, you need a subquery.
To find order info rows associated with senior customers, you can either look up the corresponding customer row for each order info row with a correlated subquery:
UPDATE widgetOrderInfo
SET extendedcost = (cost * qty) * (0.80)
WHERE (SELECT IsASenior
FROM widgetCustomer
JOIN widgetSale ON widgetCustomer.id = widgetSale.customer_id
WHERE widgetSale.id = widgetOrderInfo.salesOrderID
) = 'Y';
Or get all senior customers first, and check which order infos are in that set:
UPDATE widgetOrderInfo
SET extendedcost = (cost * qty) * (0.80)
WHERE salesOrderID IN (SELECT widgetSale.id
FROM widgetCustomer
JOIN widgetSale ON widgetCustomer.id = widgetSale.customer_id
WHERE IsASenior = 'Y');