Converting a mysql with Nested SELECT, EXIST, SELECT NEXT clauses to a python sqlalchemy statement

Question

So i have this statement

SELECT h.usd FROM historic h, block b 
WHERE UNIX_TIMESTAMP(h.timestamp) <=b.block_nTime 
AND NOT EXISTS 
(SELECT 'NEXT' FROM 
historic h2 where h2.timestamp > h.timestamp 
AND UNIX_TIMESTAMP(h2.timestamp) <=b.block_nTime) AND b.block_id = 'id'

I'm trying to convert this to a python sqlalchemy statement - this is how far i got.

from sqlalchemy import *
from sqlalchemy.sql import func
from sqlalchemy.orm import Session

#{...}

h = alias(historic)
h2 = alias(historic)

session.query(h.c.usd).filter(
and_(h.c.timestamp <= block.c.block_nTime,   
~exists(
func.next_value(Sequence(h2.c.timestamp))
).where(
and_(h2.c.timestamp > h.c.timestamp, h2.c.timestamp <= block.c.block_nTime
) & block.c.id == block_id)))

some how i get this error as well:

sqlalchemy.exc.ArgumentError: columns argument to select() must be a Python list or other iterable

Think im not using Sequence() correctly. What may the issue be?

Thanks in advance!

Answer 1

The error you get references the exists. Just wrap the parameter in a list and it should work:

Before: ~exists(func.next_value(Sequence(h2.c.timestamp)))
After: ~exists([func.next_value(Sequence(h2.c.timestamp))])