Oracle：如何总结 Oracle 中的别名列

Question

I have a query:

SELECT od.*, i.name AS item_name, (od.quantity*od.price) AS sub_total
    FROM order_details od
    JOIN items i ON od.item_id = i.item_id
    WHERE order_id = 9

It produces the following result.

Now, I want to sum up SUB_TOTAL column and I want the result as 1300 .

I've tried the following code but it doesn't work.

SELECT od.*, i.name AS item_name, (od.quantity*od.price) AS sub_total, SUM(sub_total) AS total
    FROM order_details od
    JOIN items i ON od.item_id = i.item_id
    WHERE order_id = 9

Please help.

Answer 1

That's a window SUM() - and you can't reuse the column alias, you need to repeat the expression, or use a subquery or CTE:

SELECT od.*, i.name AS item_name, (od.quantity * od.price) AS sub_total,
    SUM(od.quantity * od.price) OVER() AS total
FROM order_details od
JOIN items i ON od.item_id = i.item_id
WHERE order_id = 9

You might need to adjust the OVER() clause of the window SUM() according to your actual requirement. The above query will bring 1300 on both rows. You can use a PARTITION BY clause to divide the set of rows into groups, and/or use ORDER BY to compute a running sum.

Answer 2

Use window functions:

SELECT od.*, i.name AS item_name, (od.quantity*od.price) AS sub_total,
       SUM((od.quantity*od.price) OVER (ORDER BY order_detail_id)
FROM order_details od JOIn
     items i
     ON od.item_id = i.item_id
WHERE order_id = 9;

Note that you cannot re-use the alias; you need to repeat the calculation.