Why my if else does not give the expected output? (mySQL) - mysql

Question

I'm hoping you guys can help me in SQL because i'm a newbie iN sql. My problem is, the code does not give the expected output and i do not know how to fix that eventough i've searched through books and online resources. I have 2 tables (customer & order_status). The task is:
(1) select c_id,lname,address,city,description where c_id > 3
(2) select c_id,lname,address,o_status,item_total,remarks and update description to 'black' where c_id =3
(3)if item_total > 2, select o_status,item_total. ELse select o_status,item_total,remarks,order_no and update remarks to 'set'
So, here's the code:
#drop procedure if exists usp_GetAnything;
delimiter //
create procedure usp_GetAnything()
begin
declare total int ;
select total = item_total
from order_status;
select c_id,lname,address,city,description
from customer
where c_id > 3;
select c.c_id,c.lname,c.address,o.o_status,o.item_total,o.remarks,c.description
from customer c,order_status o
where c.c_id=o.c_id;
update customer
set description = 'black'
where c_id = 3;
if (total > 2) then
select o_status,item_total,remarks
from order_status
where item_total = total;
else
select o_status,item_total,remarks,order_no
from order_status
where item_total = total;
update order_status
set remarks = 'set';
end if;
end
I'm expecting the output to get the item_total for each row. If the item_total >2, it will just select, Else, it will update the remarks.. Each c_id have different no. of item_total.

Answer 1

Your code is a bit of a scramble, so I will try to help doing one piece at a time.
Your (1), where c_id > 3, what is the purpose of this, this will give ALL customers with ID greater than 3, but ok.
Formatting your queries for readability is also a good thing to get in the habit of. Also,
USE table aliases, especially when you get into longer table name references, makes it easier
to join/link/get fields/where/group by respectively. Even if one table.
select
c.c_id,
c.lname,
c.address,
c.city,
c.description
from
customer c
where
c.c_id > 3;
Your (2a). Your query does a simple join from the customer table to the order status based on
the customer's ID. This is ok, but it is also returning ALL customers that have an order,
and if someone has multiple orders, it will show that customer for EACH order they have.
Also, try to get in the habit of using JOIN conditions on tables instead of implied joins
within the WHERE clause. It makes it easier when you need to get into left/right join conditions.
select
c.c_id,
c.lname,
c.address,
o.o_status,
o.item_total,
o.remarks,
c.description
from
customer c
JOIN order_status o
ON c.c_id = o.c_id;
Now, if you only cared about a specific customer, add your WHERE clause for said customer ID.
Your (2b) component to update the description to 'black' where c_id =3, that was ok
update customer
set description = 'black'
where c_id = 3;
For #3, the item_total > 2. What is the basis of this item total. You had
declare total int ;
select total = item_total
from order_status;
This should not really do anything as it is going through every order and will just return
1(true) or 0(false) for every record. You have no criteria such as total per customer
or even just the number of orders for a given customer... Such as Person "A" has 5 orders on file,
and Person "B" has 1, Person "C" has 2. You will need to clarify your intent on that.
This poses the follow-up to your if/else based on the item_total > 2. select version(a) or (b)
of yet another query (not going to copy/paste that as no idea your intent)
In your if( total > 2 ) else condition, your update statement has no WHERE clause,
so it will update EVERY record in the order_status table (probably NOT what you intended).
So, with a bit more clarification, maybe some sample data myself and others could help.
Even as a newbie, if there are things that may be confidential otherwise, you can always mask
things by showing only the critical pieces, but not actually show production data, but show
sample data to help us follow your needs... now and in the future.