trigger in oracle allows insert if field is found - oracle

Question

I have three tables called products, customers and reserve_products. The trigger is on the reserve products table and will only let you insert into the table if the customer id and product id and quantity of product is found and not 0. I am having problems with the sql and checking if the rows exist.
My tables are as follows:
products
CREATE TABLE "SNAGEL"."PRODUCTS"
( "PID" NUMBER(6,0),
"PRODUCT_NAME" VARCHAR2(255 BYTE),
"QUANTITY" NUMBER,
"PRICE" NUMBER,
"PRODUCT_SIZE" VARCHAR2(255 BYTE),
"PRODUCT_VALUE" NUMBER,
PRIMARY KEY ("PID")
Customers
CREATE TABLE "SNAGEL"."CUSTOMERS"
( "CID" NUMBER(6,0),
"FIRST_NAME" VARCHAR2(30 BYTE),
"LAST_NAME" VARCHAR2(30 BYTE),
"PHONE_NUMBER" NUMBER,
PRIMARY KEY ("CID")
Reserve Product
my trigger
CREATE OR REPLACE TRIGGER reserveProductTrigger
before insert on RESERVE_PRODUCT FOR EACH ROW
DECLARE
pid products.pid%rowtype;
pidError exception;
cid customers.cid%rowtype;
cidError exception;
pidSoldout exception;
productQuantity number;
BEGIN
select cid from CUSTOMERS
where cid = :new.CID;
select COUNT(pid from products
where pid = :new.PID;
select quantity into productQuantity
from products
where pid= :new.pid;
if cid = null then
raise cidError;
elsif pid = null then
raise pidError;
elsif productQuantity = 0 then
raise pidSoldout;
else
update products
set quantity = productQuantity -1
where pid = pid;
END IF;
EXCEPTION
When cidError then
DBMS_OUTPUT.PUT_LINE('CUSTOMER not found error!');
RAISE;
When PidError then
DBMS_OUTPUT.PUT_LINE('PRODUCT not found error!');
RAISE;
When pidSoldout then
DBMS_OUTPUT.PUT_LINE('product sold out error!');
RAISE;
END;
/

Answer 1

You forgot to store the details from your select statements into the variables yoiu created for them. So try this instead:
CREATE OR REPLACE TRIGGER reserveProductTrigger
before insert on RESERVE_PRODUCT FOR EACH ROW
DECLARE
pid products.pid%type;
pidError exception;
cid customers.cid%type;
cidError exception;
pidSoldout exception;
productQuantity number;
BEGIN
BEGIN
select cid into CID
from CUSTOMERS
where cid = :new.CID;
EXCEPTION WHEN NO_DATA_FOUND THEN
raise cidError;
END;
BEGIN
select pid
, quantity
INTO PID
, productQuantity
from products
where pid = :new.PID;
EXCEPTION WHEN NO_DATA_FOUND THEN
raise pidError;
END;
if productQuantity <= 0 then -- If it goes negative you've over
raise pidSoldout; -- committed and shouldn't accept either.
else
update products
set quantity = productQuantity -1
where pid = pid;
END IF;
EXCEPTION
When cidError then
DBMS_OUTPUT.PUT_LINE('CUSTOMER not found error!');
RAISE;
When PidError then
DBMS_OUTPUT.PUT_LINE('PRODUCT not found error!');
RAISE;
When pidSoldout then
DBMS_OUTPUT.PUT_LINE('product sold out error!');
RAISE;
END;
/
However, rather than relying on the trigger to check on the existence of PID and CID, you should use referential integrity constraints. Additionally you can put a check constraint on the Quantity column in Products requiring it to be >= 0.
Then the only thing you need to do in your trigger is decrement the Quantity:
CREATE TABLE "PRODUCTS"
( "PID" NUMBER(6,0),
"PRODUCT_NAME" VARCHAR2(255 BYTE),
"QUANTITY" NUMBER CONSTRAINT PRODUCT_MIN_QUANTITY CHECK (QUANTITY >= 0), -- Add Check constraint here
"PRICE" NUMBER,
"PRODUCT_SIZE" VARCHAR2(255 BYTE),
"PRODUCT_VALUE" NUMBER,
CONSTRAINT PRODUCTS_PK PRIMARY KEY ("PID") -- Name the PK Constraint
);
CREATE TABLE "CUSTOMERS"
( "CID" NUMBER(6,0),
"FIRST_NAME" VARCHAR2(30 BYTE),
"LAST_NAME" VARCHAR2(30 BYTE),
"PHONE_NUMBER" NUMBER,
CONSTRAINT CUSTOMERS_PK PRIMARY KEY ("CID") -- Name the PK Constraint
);
create table reserve_product (
PID NOT NULL CONSTRAINT reserve_product_fk REFERENCES products(PID) -- Use referential integrity here
, CID NOT NULL CONSTRAINT reserve_product_fk REFERENCES customers(CID) -- and here
)
CREATE OR REPLACE TRIGGER reserveProductTrigger
before insert on RESERVE_PRODUCT FOR EACH ROW
BEGIN
update products
set quantity = quantity -1
where pid = :new.pid;
END;
/
Now if either PID or CID is missing from Products or Customers respectivly, or if the Products record has a quantity of 0, appropriate exceptions will be raised.

Answer 2

CREATE OR REPLACE TRIGGER trg_reserve_products
BEFORE INSERT ON reserve_products
FOR EACH ROW
DECLARE
v_count NUMBER;
v_p_id NUMBER(6);
v_c_id NUMBER(6);
v_p_quantity products.p_quantity%TYPE;
v_p_name products.p_name%TYPE;
BEGIN
SELECT COUNT(*)
INTO v_count
FROM products
WHERE p_id = :NEW.p_id;
IF v_count = 0 THEN
raise_application_error(-20000 , 'Invalid Product ID.');
END IF;
SELECT COUNT(*)
INTO v_count
FROM customers
WHERE c_id = :NEW.c_id;
IF v_count IS NULL THEN
raise_application_error(-20000 , 'Invalid Customer ID.');
END IF;
SELECT p_quantity, p_name
INTO v_p_quantity, v_p_name
FROM products
WHERE p_id = :NEW.p_id;
IF v_p_quantity < 1 THEN
raise_application_error(-20000 , v_p_name || ' 4 is currently out of stock.');
END IF;
UPDATE products
SET p_quantity = p_quantity - 1
WHERE p_id = :NEW.p_id;
END trg_reserve_products;
SELECT * FROM products;
INSERT INTO reserve_products VALUES(1, 101, 1);
INSERT INTO reserve_products VALUES(2, 46, 1);
INSERT INTO reserve_products VALUES(3, 46, 2);
INSERT INTO reserve_products VALUES(4, 46, 3);
SELECT * FROM products;
SELECT * FROM reserve_products;