MySQL update a master field only if condition is true - mysql

Question

Is there a way to update SQL in such a way, for example.
Master Table has a column called INVOICESCOUNT.
When an invoice is deleted successfully, then the INVOICESCOUNT is decreased.
For example, a SQL psuedo-code statement like this:
Delete From Invoices where INVOICE=500;
Update Customers SET INVOICECOUNT=INVOICECOUNT-1 WHERE Customer=1 (if prior statement returns 1 affected row);
I need it to be embedded within the same SQL statement instead of having the source code handling executing the 2 statements separately.
Thanks for any advice. Please also let me know if there is any minimal MySQL version requirement if there is such a solution.
UPDATE with more info: note that the list of Customers I present to the user can be very different each time, example, CustomerGroupID=? or CustomerCreated within a certain date, so the Customers query cannot be cached efficiently, as such I prefer to update the INVOICECOUNT (as it will be hit on many times in an hour by different users listing different groups of customers).

Answer 1

Better idea: instead have a VIEW that shows you Customer's invoice counts:
CREATE VIEW CustomersInfo AS
SELECT
CustomerId,
COUNT(*) AS InvoiceCount
FROM
Invoices
GROUP BY
CustomerId
;
Then you'd use it like so:
SELECT
c.CustomerId,
COALESCE( ci.InvoiceCount, 0 ) AS InvoiceCount
FROM
Customers AS c
LEFT OUTER JOIN CustomersInfo AS ci ON c.CustomerId = ci.CustomerId
(Don't use an INNER JOIN, otherwise Customers without any invoices won't be in the output).

Answer 2

You can use triggers for that
CREATE TABLE Invoices(INVOICE INT)
CREATE TABLe Customers(Customer int,INVOICECOUNT int)
INSERT INTO Customers VALUES (1,1)
CREATE TRIGGER del_after AFTER DELETE ON Invoices
FOR EACH ROW
Update Customers SET INVOICECOUNT=INVOICECOUNT-1 WHERE Customer=1
Delete From Invoices where INVOICE=500;
SELECT * FROM Customers
Customer | INVOICECOUNT
-------: | -----------:
1 | 1
INSERT INTO Invoices VALUES (400)
Delete From Invoices where INVOICE=500;
SELECT * FROM Customers
Customer | INVOICECOUNT
-------: | -----------:
1 | 1
INSERT INTO Invoices VALUES (500)
Delete From Invoices where INVOICE=500;
SELECT * FROM Customers
Customer | INVOICECOUNT
-------: | -----------:
1 | 0
db<>fiddle here

Answer 3

As was mentioned in the comments, you probably don't need to store the invoice count in a table column, however if you MUST have the invoice count column for any reason your best bet might be a stored procedure.
DELIMITER //
CREATE PROCEDURE removeinvoice
BEGIN
DELETE FROM invoices WHERE invoice=500;
UPDATE customers SET invoicecount = (SELECT COUNT(*) FROM invoices);
END//
DELIMITER ;
Then you just call that stored procedure.
CALL removeinvoice;