SQL Help

Hi. I am having problems with my coding for the following project.

On problems 2 and 3 Im getting a Missing Expression error and on 4 im getting a Not a group by expression error. Can someone take a look at my code and show me how to fix this?

oh and as a word of note. For problem 2 and 3 it says the error is on line 3 and for question 4 it says its on line 2.

Thanks

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-- LAB #4. -- In this lab, we keep track of the books for a lending library.
--
-- Template SQL file for HW4
--

Spool c:sqlhw4.lst;
Set echo on;
set pagesize 55;
set linesize 100;

--Use count function to find out how many customers are in each state.

select USER_NAME, TO_CHAR(SYSDATE,'MM/DD/YY HH24:MI') as "Lab Run Time"
from PVF_USER;

select state, count (customer_id) as "State Customers"
from customer
group by state
order by state;


-- 2. What is the total sales amount per day?
-- sort by Order_date

column "Sales Amount" format $9,999;
column "Customer Name" format a20;
column "Product Name" format a20;
column "Order Date" format a10;

select oh.order_date,
sum(ol.quantity * p.unit_price) as "Sales Amount",
from order_hdr oh, order_line ol, product p
where oh.order_id = ol.order_id and
ol.product_id = p.product_id
group by oh.order_date
order by oh.order_date;

-- 3. How much each customer has spent?
-- Sort by Customer_name

select c.customer_name,
sum(ol.quantity * p.unit_price) as "Sales Amount",
from customer c, order_hdr oh, order_line ol, product p
where c.customer_id = oh.customer_id and
oh.order_id = ol.order_id and
ol.product_id = p.product_id
group by c.customer_name
order by c.customer_name;


-- 4. What is the total amount and total quantity of each product ordered by each customer?
-- sort by Customer_name

select c.customer_name,
p.product_id,
p.product_name,
sum(ol.quantity * p.unit_price) as "Sales Amount",
sum(ol.quantity) as "Total Quantity"
from customer c, order_hdr oh, order_line ol, product p
where c.customer_id = oh.customer_id and
oh.order_id = ol.order_id and
ol.product_id = p.product_id
group by c.customer_name
order by c.customer_name;


-- 5. What is the total amount and total quantity of each product for each day?
-- sort by Order_date, Customer_name

select oh.order_date,
c.customer_name,
p.product_id,
p.product_name,
oh.order_date,
sum(ol.quantity * p.unit_price) as "Sales Amount",
sum(ol.quantity) as "Total Quantity"
from customer c, order_hdr oh, order_line ol, product p
where c.customer_id = oh.customer_id and
oh.order_id = ol.order_id and
ol.product_id = p.product_id
group by c.customer_name, p.product_id, p.product_name,
oh.order_date
order by oh.order_date, c.customer_name;



spool off;
set echo off;

Hi!
It's really hard to find errors without looking at the corresponding data. Could you provide some sample data sets from the actual tables here? That would help.