Creating a trigger to adjust product stock - APEX ORACLE - sql

Question

I'm trying to create a trigger on APEX ORACLE so that when a purchase goes through the orderline table, the quantity that is set when the customer buys the products is taken off the stock in the products table.
CREATE or Replace TRIGGER updatestock
AFTER DELETE OR UPDATE OF QUANTITY.ORDERLINE ON ORDERLINE
FOR EACH ROW
BEGIN
SET PRODUCT_STOCK.PRODUCTS = PRODUCT_STOCK.PRODUCTS - QUANTITY.ORDERLINE
WHERE PRODUCT_ID.ORDERLINE = PRODUCT_ID.PRODUCTS
END;
Basically I want the trigger to notice the quantity in the orderline and minus it from the product stock. However, I get the following error:
ORA-01748: only simple column names allowed here
Could anyone point me in the right direction?
SQL:
DROP TABLE ADMIN CASCADE CONSTRAINTS ;
DROP TABLE USERS CASCADE CONSTRAINTS ;
DROP TABLE STALLS CASCADE CONSTRAINTS ;
DROP TABLE PRODUCTS CASCADE CONSTRAINTS ;
DROP TABLE STALLHOLDER CASCADE CONSTRAINTS ;
DROP TABLE CUSTOMERORDER CASCADE CONSTRAINTS;
DROP TABLE ORDERLINE CASCADE CONSTRAINTS;
DROP TABLE COLLECTION CASCADE CONSTRAINTS;
drop sequence ADMIN_ID_SEQ;
drop sequence USER_ID_SEQ;
drop sequence STALL_ID_SEQ;
drop sequence PRODUCT_ID_SEQ;
drop sequence STALLHOLDER_ID_SEQ;
drop sequence CUSTOMERORDER_ID_SEQ;
drop sequence ORDERLINE_ID_SEQ;
drop sequence COLLECTION_ID_SEQ;
create sequence ADMIN_ID_SEQ start with 1;
create sequence USER_ID_SEQ start with 1;
create sequence STALL_ID_SEQ start with 1;
create sequence PRODUCT_ID_SEQ start with 1;
create sequence STALLHOLDER_ID_SEQ start with 1;
create sequence CUSTOMERORDER_ID_SEQ start with 1;
create sequence COLLECTION_ID_SEQ start with 1;
create sequence ORDERLINE_ID_SEQ start with 1;
CREATE table COLLECTION (
COLLECTION_ID NUMBER(20) NOT NULL PRIMARY KEY,
STATUS VARCHAR(10) NOT NULL,
TIME NUMBER(4) NOT NULL);
CREATE table CUSTOMERORDER (
ORDER_ID NUMBER(15) NOT NULL PRIMARY KEY,
ORDER_DATE NUMBER(8) NOT NULL,
STATUS VARCHAR2(10) NOT NULL,
COLLECTION_ID NUMBER(20) NOT NULL);
CREATE TABLE STALLS (
STALL_ID NUMBER(15) NOT NULL PRIMARY KEY,
STALL_NAME VARCHAR(25) NOT NULL,
STALL_DESC VARCHAR(100),
STALL_TYPE VARCHAR(25) NOT NULL,
STALLHOLDER_ID NUMBER(25) NOT NULL);
CREATE TABLE PRODUCTS (
PRODUCT_ID NUMBER(15) NOT NULL PRIMARY KEY,
PRODUCT_NAME VARCHAR(25) NOT NULL,
PRODUCT_TYPE VARCHAR(15) NOT NULL,
PRODUCT_PRICE NUMBER(6,2) NOT NULL,
PRODUCT_STOCK NUMBER(3) NOT NULL,
STALL_ID NUMBER(15) NOT NULL);
CREATE table ORDERLINE (
ORDERLINE_ID NUMBER(15) NOT NULL PRIMARY KEY,
QUANTITY NUMBER(2) NOT NULL,
TOTALPRICE DECIMAL(19,4) NOT NULL,
ORDER_ID NUMBER(15) NOT NULL,
PRODUCT_ID NUMBER(15) NOT NULL);
CREATE table USERS (
USER_ID NUMBER(15) NOT NULL PRIMARY KEY,
USERNAME VARCHAR2(25) NOT NULL,
PASSWORD VARCHAR2(25) NOT NULL,
NAME VARCHAR2(25) NOT NULL,
SURNAME VARCHAR2(25) NOT NULL,
ADDRESS VARCHAR2(100) NOT NULL,
CONTACTNO NUMBER(11) NOT NULL);
CREATE table STALLHOLDER (
STALLHOLDER_ID NUMBER(25) NOT NULL PRIMARY KEY,
USERNAME VARCHAR2(25) NOT NULL,
PASSWORD VARCHAR2(25) NOT NULL,
NAME VARCHAR2(25) NOT NULL,
SURNAME VARCHAR2(25) NOT NULL,
CONTACTNO NUMBER(11) NOT NULL);
CREATE table ADMIN (
ADMIN_ID NUMBER(15) NOT NULL PRIMARY KEY,
USERNAME VARCHAR2(25) NOT NULL,
PASSWORD VARCHAR2(25) NOT NULL);
INSERT INTO ADMIN VALUES (ADMIN_ID_SEQ.nextval, 'Test', 'Test');
INSERT INTO ADMIN VALUES (ADMIN_ID_SEQ.nextval, 'Admin', 'Admin');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder1', 'Stallholder1', 'Stall 1', 'Stall 1', '0');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder2', 'Stallholder2', 'Stall 2', 'Stall 2', '0');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder3', 'Stallholder3', 'Stall 3', 'Stall 3', '0');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder4', 'Stallholder4', 'Stall 4', 'Stall 4', '0');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder5', 'Stallholder5', 'Stall 5', 'Stall 5', '0');
INSERT INTO STALLHOLDER VALUES (STALLHOLDER_ID_SEQ.nextval, 'Stallholder6', 'Stallholder6', 'Stall 6', 'Stall 6', '0');
INSERT INTO USERS VALUES (USER_ID_SEQ.nextval, 'Test', 'Test', 'Test', 'Test', 'Test', '0');
INSERT INTO USERS VALUES (USER_ID_SEQ.nextval, 'Test2', 'Test2', 'Test2', 'Test2', 'Test2', '0');
INSERT INTO USERS VALUES (USER_ID_SEQ.nextval, 'Test3', 'Test3', 'Test3', 'Test3', 'Test3', '0');
INSERT INTO USERS VALUES (USER_ID_SEQ.nextval, 'Test4', 'Test4', 'Test4', 'Test4', 'Test4', '0');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Meat Store', '', 'Meat', '1');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Meat Store 2', '', 'Meat', '2');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Confectionary Store', '', 'Confectionary', '3');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Confectionary Store 2', '', 'Confectionary', '4');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Clothing Store', '', 'Clothing', '5');
INSERT INTO STALLS VALUES (STALL_ID_SEQ.nextval, 'Phone Store', '', 'Clothing', '6');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '5.99', '15', '0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '9.99', '10','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '12.99', '10','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '3.99', '20','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '5.99', '20','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '8.99', '15','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '1.99', '20','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '2.99', '20','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '3.99', '20','0', '1');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '5.99', '15','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '9.99', '20','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Steak', 'Meat', '12.99', '20','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '3.99', '15','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '5.99', '15','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Pork', 'Meat', '8.99', '15','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '1.99', '20','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '2.99', '20','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Bacon', 'Meat', '3.99', '20','0', '2');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Haribo', 'Sweets', '1.50', '50','0', '3');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Haribo', 'Sweets', '1.00', '50','0', '3');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'PicknMix100g', 'Sweets', '2.00', '999','0', '3');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'PicknMix200g', 'Sweets', '3.50', '999','0', '3');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'ToxicWaste', 'Sweets','1.50','50','0','3');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Haribo', 'Sweets', '1.50', '100','0', '4');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Haribo', 'Sweets', '1.00', '100','0', '4');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'PicknMix100g', 'Sweets', '2.00', '999','0', '4');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'PicknMix200g', 'Sweets', '3.50', '999','0', '4');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'ToxicWaste', 'Sweets', '1.50', '50','0', '4');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'T-Shirts', 'Clothing', '10.00', '20','0', '5');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Shorts', 'Clothing', '15.00', '20','0', '5');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Jeans', 'Clothing', '20.00', '20','0', '5');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Hoodies', 'Clothing', '20.00', '20','0', '5');
INSERT INTO PRODUCTS VALUES (PRODUCT_ID_SEQ.nextval, 'Vests', 'Clothing', '10.00', '20','0', '5');
ALTER TABLE STALLS ADD CONSTRAINT FK_STALLHOLDER_ID FOREIGN KEY (STALLHOLDER_ID) REFERENCES STALLHOLDER(STALLHOLDER_ID);
ALTER TABLE ORDERLINE ADD CONSTRAINT FK_ORDER_ID FOREIGN KEY (ORDER_ID) REFERENCES CUSTOMERORDER(ORDER_ID);
ALTER TABLE ORDERLINE ADD CONSTRAINT FK_PRODUCT_ID FOREIGN KEY (PRODUCT_ID) REFERENCES PRODUCTS(PRODUCT_ID);
ALTER TABLE CUSTOMERORDER ADD CONSTRAINT FK_COLLECTION_ID FOREIGN KEY (COLLECTION_ID) REFERENCES COLLECTION(COLLECTION_ID);
ALTER TABLE PRODUCTS ADD CONSTRAINT FK_STALL_ID FOREIGN KEY (STALL_ID) REFERENCES STALLS(STALL_ID);
​

Answer 1

The error is presumably coming from the OF QUANTITY.ORDERLINE because you're using a table.column pattern rather than just the column name. You also seem to be consistently putting the table and column names the wrong way around, and you're missing the UPDATE before SET, and you are trying to refer to columns in the table row you're updating rather than using the NEW pseudorow. So this should be closer:
CREATE or Replace TRIGGER updatestock
AFTER DELETE OR UPDATE OF QUANTITY ON ORDERLINE
FOR EACH ROW
BEGIN
UPDATE PRODUCTS
SET PRODUCT_STOCK = PRODUCT_STOCK - :NEW.QUANTITY
WHERE PRODUCT_ID = :NEW.PRODUCT_ID
END;
But NEW values are null on delete; you aren't doing any adjustment in insert; and even on update you maybe want to be taking both the old and new quantity into account.
Even then trying to maintain a running total in another table only really works in a single-user system, or where updates are serialised. If two people update the same orderline row at the same time, the trigger will apply both updates to the products table, but the second will block until the first has committed, and will be applied to the old value at the start of that statement - so you'll lose the first update, effectively.