SQL Query SELECT and Group by with conditions - mysql

Question

I have a table called item table.
Sample contents:
order product plan qty price term base_price
CO0300039921 ZZFEE0000 N 1 0.01 1 25
CO0300039921 ZZFEE0000 N 1 0.01 1 37.13
CO0300039921 ZZFEE0000 N 1 0.02 1 37.13
CO0300039921 ZZFEE0000 Y 1 0 1 1
CO0300039921 ZZFEE0000 Y 1 0 1 1
AO1000301407 VOSVC0002W0 Y 1 0 1 3
AO1000301407 VOACT0101 N 1 0 2 5.99
If plan is ‘N’ Then
get SUM(qty) AS 'quantity'
get price AS 'rate'
If plan is ‘Y’ Then
get SUM(qty) AS 'quantity'
get (term * qty) AS 'rate'
get (base_price) AS 'base'
FROM item
WHERE order = 'CO0300039921'
GROUP BY product, price, base_price
EXPECTED RESULT:
order product plan qty price rate base_price
CO0300039921 ZZFEE0000 N 2 0.01 0.01 -
CO0300039921 ZZFEE0000 N 1 0.02 1 -
CO0300039921 ZZFEE0000 Y 2 - 1 1
Here is what I've tried:
SELECT CASE WHEN p8_plus_plan = 'Y' THEN
(
SUM(qty_ordered),
(p8_contract_term*qty_ordered) AS 'rate',
product_base_price
)
ELSE
(
SUM(qty_ordered),
price AS 'rate'
)
END
FROM ns_order_line
WHERE order_no = ?
GROUP BY product_id, price, p8_plus_plan, product_base_price, order_no;
But I'm having an error. Please help.

Answer 1

You would do this using conditional aggregation. Something like this:
select sum(case when plan = 'N' then qty end) as N_qty,
sum(case when plan = 'N' then price end) as N_rate,
sum(case when plan = 'Y' then qty end) as Y_qty,
sum(case when plan = 'Y' then term*qty end) as Y_rate,
sum(case when plan = 'Y' then base_price end) as Y_base
from item
where order = 'CO0300039921'
group by product;
I'm not sure what you really want to aggregate by. But the key idea where is the case inside the aggregation functions.

Answer 2

Something like this I imagine.
SELECT
`order`
, `product`
, `plan`
, CASE WHEN `plan` = 'Y' THEN base_price END AS base /* edit due to comment */
, SUM(qty) AS qty
, MAX(price) AS price
, SUM(CASE WHEN `plan` = 'N' THEN price
WHEN `plan` = 'Y' THEN (term * qty) END) AS rate
FROM item
WHERE `order` = 'CO0300039921'
GROUP BY
`order`
, `product`
, `plan`
, CASE WHEN `plan` = 'Y' THEN base_price END
btw: The column name "order" is not a good choice as it is a reserved word and very frequently used too. You need to use backticks when referencing that column.
It is possible to use a CASE EXPRESSION without an aggregate function, BUT that case expression then must* also be part of he GROUP BY clause.
*In MySQL (only) you can bypass this because MySQL has an unusual "extension" to group by syntax but this can be changed by server settings and relying on that extension is risky. I strongly urge you to include all columns (including case expressions) into the group by clause that do NOT use an aggregate function (sum/count/avg etc.)