final clause

[sdrenn]

FINAL modifier added
https://clickhouse.tech/docs/ru/query_language/select/#select-from-final

[coveralls]

Coverage increased (+0.08%) to 92.109% when pulling 5534f3e on sdrenn:final-clause into 2f79283 on xzkostyan:master.

[xzkostyan]

Good job!

[ods]

How does it work for JOIN-s, select from what table will be FINAL-ized?

And why not just use standard SQLAlchemy way for such cases with_hint() method? It requires just 2 lines in compiler:

    def get_from_hint_text(self, table, text):
        return text

Usage:

table.select().with_hint(table, 'FINAL')

[xzkostyan]

It seems than FINAL clause makes sense only in selecting from single table with *mergetree engine.

According to docs FINAL clause should be rendered after FROM .... and before any JOINs.

Currently FINAL will be rendered after JOINs:

q1 = self.session.query(table.c.x).subquery()
q2 = self.session.query(table.c.x).subquery()

print(self.session.query(q1.c.x, q2.c.x).join(q2, q1.c.x == q2.c.x).final())

SELECT anon_1.x AS anon_1_x, anon_2.x AS anon_2_x FROM (SELECT t1.x AS x FROM t1) AS anon_1 INNER JOIN (SELECT t1.x AS x FROM t1) AS anon_2 ON anon_1.x = anon_2.x FINAL

Which is obviously incorrect. But even it will render in proper place ClickHouse server will throw error:

:) select * from (select number as x from system.numbers limit 10) as a final join (select number as x from system.numbers limit 10) as b on a.x = b.x;

SELECT *
FROM 
(
    SELECT number AS x
    FROM system.numbers
    LIMIT 10
) AS a
FINAL
INNER JOIN 
(
    SELECT number AS x
    FROM system.numbers
    LIMIT 10
) AS b ON a.x = b.x

Received exception from server (version 20.3.2):
Code: 181. DB::Exception: Received from localhost:9000. DB::Exception: Illegal FINAL. 

0 rows in set. Elapsed: 0.005 sec. 

In both cases we will get an error.

Yes, with_hint can be used for FINAL rendering. But it's designed for other purposes. It is flexible (I believe that hints are escaped) but imho .final() looks way more natural.

[ods]

In both cases we will get an error.

It does work when properly formed. At least the following test passes: https://github.com/ods/aiochsa/blob/master/tests/test_execute.py#L306-L332

[xzkostyan]

Oh, I see. Now I understand your point. #95