MYSQL trying to get other attributes from max value - mysql

Question

I have this trigger
DELIMITER $$
CREATE TRIGGER before_bid_insert
BEFORE INSERT ON Bids
FOR EACH ROW
BEGIN
IF NEW.amount > (SELECT B.amount, B.vin FROM Bids B WHERE B.vin = NEW.vin AND B.amount = (SELECT MAX(amount) from Bids)) THEN
INSERT INTO Notifications (buyer, outbidded, vin, amount) values (NEW.buyer, B.buyer, NEW.vin, NEW.amount);
END IF ;
END$$
DELIMITER ;
With tables
CREATE TABLE Auctions
(seller VARCHAR(100),
vin VARCHAR(20),
brand VARCHAR(20),
cartype VARCHAR(20),
model VARCHAR(20),
color VARCHAR(20),
minprice int,
dt DATETIME,
PRIMARY KEY (vin, seller)
);
CREATE TABLE Bids
(buyer VARCHAR(20),
vin VARCHAR(20),
amount int,
autobid int,
upperlimit int,
PRIMARY KEY(buyer, vin, amount),
FOREIGN KEY (vin) REFERENCES Auctions(vin)
);
CREATE TABLE Notifications
(buyer VARCHAR(20),
outbidded VARCHAR(20),
vin VARCHAR(20),
amount int,
PRIMARY KEY(vin, buyer),
FOREIGN KEY (vin) REFERENCES Bids(vin),
FOREIGN KEY (buyer) REFERENCES Bids(buyer)
);
However whenever I run it, it says operand should contain 1 columns.
What i'm trying to do is, if the row thats being inserted has a higher amount value than any row already in the bids table with the same VIN as the new row, then insert the values into notifications.

Answer 1

You can do this to help with both your issues:
SELECT B.amount INTO #amount, B.buyer INTO #buyer
FROM Bids B WHERE B.vin = NEW.vin AND B.amount = (SELECT MAX(amount) from Bids)
IF NEW.amount > #amount THEN
INSERT INTO Notifications (buyer, outbidded, vin, amount)
values (NEW.buyer, #buyer, NEW.vin, NEW.amount);
Also, not sure but I feel you should have another check in SELECT MAX(amount) from Bids query to include a WHERE clause to check for vin.