SELECT 从 SQL 客户端执行时返回行，但从 SQLAlchemy 执行时返回行

Question

I have the following query:

SELECT sum(x), sum(y)
FROM stats s1
WHERE fk_id = :id
AND EXISTS (
  SELECT
  FROM stats s2
  WHERE s2.fk_id = s1.fk_id
  AND s2.datetime::date = (now() - '1 day'::interval)::date
)

The second condition ensures that there are stats from yesterday. Otherwise it returns no results.

When I execute it from a SQL client (ie DBeaver), it returns 1 row as expected, eg 12.3, 45.6 . When I execute the query from SQLAlchemy, ie session.execute(query, {"id": id}).first() , it returns (None, None) . Same query, same database, same id.

I tried running it from SQLAlchemy without the EXISTS condition , and in this case, it returns 1 row. So it's something related to the second condition when executed from different places.

Why does the EXISTS condition return TRUE when executed from a SQL client but FALSE from SQLAlchemy?

Answer 1

You must SELECT something, even in a subquery, even if it makes no sense:

---

SELECT SUM(s1.x), SUM(s1.y)
FROM stats s1
WHERE s1.fk_id = :id
AND EXISTS (
  SELECT 'OMG!' -- <<-- HERE
  FROM stats s2
  WHERE s2.fk_id =  s1.fk_id
  AND s2.datetime::date = (now() - '1 day'::interval)::date
  )
  ;