Moshe C. wrote:
> How do I write an expression (in sqlalchemy 0.4.6) that will generate
> the following expression:
>
> select count(distinct field1, field2) from tableA;
>
> I know how to do it for one field and I know how to do it with no
> count using distinct=True, but not this combination.
>
What database are you using? I have not heard of a dialect that accepts
multiple columns in a COUNT() function. This seems to work on 0.4.6, but
it is sheer luck and very fragile:
>>> print select([func.count(tableA.c.field1.distinct(),
tableA.c.field2)], from_obj=tableA)
SELECT count(DISTINCT "tableA".field1, "tableA".field2) AS count_1
FROM "tableA"
The "standard" way is to use a subquery like so:
select count(*) from (select distinct field1, field2 from tableA) anon
which you can do via:
>>> print select([func.count(text("*"))],
from_obj=select([tableA.c.field1, tableA.c.field2], distinct=True))
SELECT count(*) AS count_1
FROM (SELECT DISTINCT "tableA".field1 AS field1, "tableA".field2 AS field2
FROM "tableA")
Hope it helps,
-Conor
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