update table pl/sql - sql

Question

I would like to update the following table using pl/sql function, the thing is I managed to write a trigger code but I want to re-write it using 'function' instead.
I would like for Customer 5 to increase their order from 30 to 200. and Enable the user to type in:
1) The number 5 for customer_ID and
2) 200 for the updated quantity.
and print out the total quantity for customer 5 before and after the update.
Create table sales (customer_ID number(10), product_ID number(10), quantity number(10));
INSERT INTO sales (customer_ID, product_ID, quantity) Values(3,1,23);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(1,2,34);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(1,3,654);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(3,7,32);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(4,3,23);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(3,3,111);
INSERT INTO sales (customer_ID, product_ID, quantity) Values(5,4,6);
Trigger code I wrote:
create or replace trigger quantity_change
before insert or update of quantity on sales
for each row
WHEN (NEW.customer_id > 0)
DECLARE
qua number;
BEGIN
qua := :NEW.quantity - :OLD.quantity;
dbms_output.put_line('Old quangtity: ' || :OLD.quantity);
dbms_output.put_line('New quantity: ' || :NEW.quantity);
dbms_output.put_line('diiference quangtity: ' || qua);
END;
UPDATE sales
SET quantity = 200 WHERE customer_id = 5;
I managed to write this procedure but still stuck, dont know how to enable use
CREATE or replace PROCEDURE Updatesales
(
customer_ID number,
product_ID number,
quantity number)
AS
BEGIN
UPDATE sales
SET quantity= 100
WHERE customer_id= 4;
END;
I want to use a function to solve the issue , a function would be somthing like this
CREATE [OR REPLACE] FUNCTION function_name [(parameter_name [IN | OUT | IN OUT] type [, ...])]
RETURN return_datatype {IS | AS} BEGIN < function_body > END [function_name];
Please advice

Answer 1

Your procedure isn't using the parameters you have declared; the body should be more like:
UPDATE sales
SET quantity= quantity
WHERE customer_id= customer_id;
... but that won't do what you expect because you've used the same names for the parameters and columns (and haven't referenced the product ID at all), so every row in the table will be updated with its current value. It's common to use a prefix for your formal parameter names to avoid that confusion, though you can also use the procedure name explicitly when you refer to them.
You said you want a function but it isn't clear why. It's conventional to modify data in procedures and not in functions, and if a function does do any DML then it can't be called from a query and would have to be called in a PL/SQL context. So I'll start with a procedure.
You said you wanted to 'print out' the quantity before and after the update. The procedure shouldn't do that; you should not assume that the user or client can handle dbms_output or will have it enabled. You could use an OUT parameter to return the pre-update value to the caller though:
CREATE OR REPLACE PROCEDURE update_sales
(
p_customer_id IN sales.customer_id%type,
p_product_id IN sales.product_id%type,
p_new_quantity IN sales.quantity%type,
p_old_quantity OUT sales.quantity%type
) AS
BEGIN
SELECT quantity
INTO p_old_quantity
FROM sales
WHERE customer_id = p_customer_id
AND product_id = p_product_id
FOR UPDATE;
UPDATE sales
SET quantity = p_new_quantity
WHERE customer_id = p_customer_id
AND product_id = p_product_id;
END;
/
This gets the current value of the quantity into an OUT variable, and also locks the record with for update to stop the value changing while you're working on it (probably overkill here, but you want to learn...)
It then updates the same row with the new value that was passed in. That is finding the row again using the customer and product IDs, and you could do that differently if you want to experiment - get the rowid into another local variable from your first query and use that for the update, or use a cursor, etc.
You could call it from an anonymous block as a test, and use dbms_output to show the old and new values; again, don't use dbms_output in production code, only for debugging:
SET serveroutput ON
DECLARE
l_customer_id sales.customer_id%type;
l_product_id sales.product_id%type;
l_new_quantity sales.quantity%type;
l_old_quantity sales.quantity%type;
BEGIN
l_customer_id := 5;
l_product_id := 4;
l_new_quantity := 200;
update_sales(l_customer_id, l_product_id, l_new_quantity, l_old_quantity);
dbms_output.put_line('Quantity changed from ' || l_old_quantity
|| ' to ' || l_new_quantity
|| ' (' || to_char(l_new_quantity - l_old_quantity, 'FMS999') || ')');
END;
/
PL/SQL procedure successfully completed.
Quantity changed from 6 to 200 (+194)
You can call this from an application, using bind variables, in a similar way, and have the application display the values.
Note that I haven't committed or rolled back the changes, and another session trying to call the procedure with the same values will block until I do; but will then see the new value (200) when it does run. I also haven't done any validation or exception handling in the procedure, so the caller needs to do both.
You could make this a function that returns the old value instead of using an OUT parameter, but you'd need to call it in a similar way, and generally people don't expect functions to change anything - just to return the current state. But if this is really how you want to do it, you need to modify the declaration to have a return type and local variable; select the old value into that local variable; and then return that too:
CREATE OR REPLACE FUNCTION update_sales
(
p_customer_id IN sales.customer_id%type,
p_product_id IN sales.product_id%type,
p_new_quantity IN sales.quantity%type
)
RETURN sales.quantity%type
AS
l_old_quantity sales.quantity%type;
BEGIN
SELECT quantity
INTO l_old_quantity
FROM sales
WHERE customer_id = p_customer_id
AND product_id = p_product_id;
UPDATE sales
SET quantity = p_new_quantity
WHERE customer_id = p_customer_id
AND product_id = p_product_id;
RETURN l_old_quantity;
END;
/
You still have to call it from a PL/SQL context (or something like a JDBC callable statement):
DECLARE
l_old_quantity sales.quantity%type;
BEGIN
l_old_quantity := update_sales(5, 4, 200);
dbms_output.put_line('Quantity was ' || l_old_quantity);
END;
/
PL/SQL procedure successfully completed.
Quantity was 6
You can't call it from plain SQL because it is doing a DML operation:
select update_sales(5, 4, 200) from dual;
Error report -
SQL Error: ORA-14551: cannot perform a DML operation inside a query
ORA-06512: at "MY_SCHEMA.UPDATE_SALES", line 17
14551. 00000 - "cannot perform a DML operation inside a query "
*Cause: DML operation like insert, update, delete or select-for-update
cannot be performed inside a query or under a PDML slave.
*Action: Ensure that the offending DML operation is not performed or
use an autonomous transaction to perform the DML operation within
the query or PDML slave.

Answer 2

What I have understood from your question is that you want to automatically update the quantity of the customer 5 to 200 whenever a new record is inserted in the SALES Table.
Trigger Code:-
CREATE OR REPLACE TRIGGER quantity_change
before insert on sales
for each row
WHEN (NEW.customer_id > 0)
DECLARE
var number;
BEGIN
var:=update_sales(:new.customer_id,:new.quantity);
:new.quantity:=var;
END;
Function Code:-
CREATE OR REPLACE FUNCTION update_sales(CUSTOMER_ID NUMBER,ORIG_QUANT NUMBER) RETURN NUMBER IS RETURNVALUE NUMBER;
BEGIN
IF customer_id = 5 THEN
returnvalue:=200;
RETURN returnvalue;
ELSE
returnvalue:= orig_quant;
RETURN returnvalue;
END IF;
END;
Sorry if I understood it otherwise.
Regards
Andy

Answer 3

To update a table you could use for example:
CREATE OR REPLACE PROCEDURE Updatesales(
xCustomer_ID IN Table1.custumerId%TYPE,
xProduct_ID IN Table1.productId%TYPE,
xQuantity IN Table1.quantity%TYPE)
AS
BEGIN
UPDATE sales
SET quantity = xQuantity
WHERE customer_id = xCustomer_ID;
COMMIT;
END;
/
To call this procedure you use:
Updatesales(4, 25, 100);

Answer 4

So what now I have done is I am calling a function from a procedure (created procedure as I as was not able to print all of the three values ), have made some assumptions from my side.
create or replace FUNCTION QUANTITY_CHANGE_NEW (CUSTOMER NUMBER, QUANT NUMBER) RETURN NUMBER
IS PRAGMA AUTONOMOUS_TRANSACTION;
old_quantity NUMBER;
BEGIN
select quantity into old_quantity from sales where customer_id=customer and rownum=1;
update sales set quantity=quant where customer_id= customer;
COMMIT;
RETURN old_quantity;
END;
CREATE OR REPLACE PROCEDURE PROCEDURE1(customer IN NUMBER, new_quantity IN NUMBER) IS
var1 NUMBER;
BEGIN
dbms_output.put_line('Customer Id is ' || customer);
var1 := QUANTITY_CHANGE_NEW(customer,new_quantity);
dbms_output.put_line('old quantity is '|| var1);
dbms_output.put_line('New quantity is '|| new_quantity);
END;
Regards
Andy