Query to list every line item but only list total once - sql

Question

We have a sales report that pulls data from multiple tables and my query shows correct data except orders that have multiple line items, i.e., the Total from the Orders table is listed on every line item row.
How can we list the Order Total only once on the row that has the smallest line item ID (for that order) but still list every line item row? Thanks!
Data Structure:
Orders Table:
Order_ID
Total
Line Items Table:
ID
Order_ID
Line_Item_Price
Line_Item_Qty
Result should be:
Order_ID Total Line_Item_Price Line_item_Qty Line_Item_ID
---------- ------- ----------------- --------------- --------------
10001 200 100 2 32001
10002 150 150 1 32002
10003 210 55 1 32003
10003 30 2 32004
10003 95 1 32005
10004 125 125 1 32006

Answer 1

This should be done in the application not in SQL.
But you can do that using window functions
select o.order_id,
case row_number() over (partition by o.order_id order by line_item_id)
when 1 then o.total
end as total,
li.line_item_price,
li.line_item_qty,
li.line_item_id
from orders o
join line_item li on o.order_id = li.order_id
order by o.order_id, li.line_item_id;
row_number() assigns a unique row number for each line item for every order. When the number is 1 the total is displayed, otherwise it's not.
In a relational database there is no such thing as "the first row" unless you specify an order by - in this case the "first row" is the line item with the smallest line_item_id
Online example: http://rextester.com/TQOIX50171
Unrelated, but: storing the total in the orders table is not a terribly good idea. In a normalized design you shouldn't store information that can easily be derived from existing data.

Answer 2

What this does is get the orders with their items and ranks them. So that the smallest item_id is rank 1 for that order, and the latest is the last rank.
ROW_NUMBER() is the function that gives the index of the rows in the output of the query (row 1 = 1, row 2 = 2). Then we can combine this with OVER (PARTITION BY), which means get the row numbers within a certain window, a partition. In this case we want to number the rows for the windows of Order_IDs. We use ORDER BY alongside to say how we order the rows within the window
When we have this table, we can then write a query on it to show the total only on the rows where the item_rank = 1
WITH rank_items_for_orders AS (
SELECT
Order_ID,
Line_Item_Price,
Line_Item_Qty,
Line_Item_ID,
Total,
ROW_NUMBER()
OVER (PARTITION BY Order_ID, ORDER BY Line_Item_ID ASC)
AS order_the_items_IDs
FROM orders o
LEFT JOIN line_items li ON o.order_id = li.order_id
ORDER BY Order_ID ASC)
SELECT
Order_ID,
Line_Item_Price,
Line_Item_Qty,
Line_Item_ID,
CASE WHEN order_the_items_IDs = 1
THEN Total ELSE NULL END
AS Total
FROM
rank_items_for_orders