Re: How to update a table with the result of deleting rows in another table

> On 6 Oct 2020, at 7:37, Hemil Ruparel <hemilruparel2002(at)gmail(dot)com> wrote:
>
> I am trying to delete orders for a given customer on a given date and add the cost of those orders to credit for the customer.
>
> So far, I came up with this:
> ```
> with data as (
> delete from orders
> where customer_id = <customer id>
> and date = '2020-10-05' returning price
> ), total as (
> select sum(price) from data
> )
> update paymentdetail
> set temp_credit = temp_credit + (select * from total)
> where customer_id = <customer id>
> ```
>
> which works. but is there a better way to update one table using the result of deleting rows from another table given that I only want the aggregate of the result?

Adding the customer id to your returning clause and using update..from could help:

with data as (
delete from orders
where customer_id = <customer id>
returning customer_id, price
), total as (
select customer_id, sum(price) as total_price
from data
group by customer_id
)
update paymentdetail
set temp_credit = temp_credit + total.total_price
from total
where customer_id = total.customer_id

You could also do this using subqueries instead of CTE’s, that may perform better as CTE’s act as optimisation fences.

Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.