来自其他 SELECT 的变量 LIMIT

Question

I got a table av with the columns ID, amount .

Also got a users table with the columns ID, timestamp

Now each voucher relates to the first x users (ordered by timestamp), where x is the amount value of the certain voucher.

I did a dbfiddle with a small example

My expected result:

voucherID    userID
11           10
12           10
12           11

For better understanding:

An admin creates a voucher that is supposed to go to the first X users registered. Each voucher has a different X

Answer 1

I think this is what you want:

with
u as (
  select userID, timestampMock, 
    row_number() over (order by timestampMock) as rn
  from users
)
select
  av.voucherID, u.userID
from av
join u on u.rn <= av.amount
order by av.voucherID, u.userID

I tested it in your dbfiddle and its result is:

voucherID   userID
---------   ------
11          10
12          10
12          11