[Answer]-Django using .extra() got error `only a single result allowed for a SELECT that is part of an expression`

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The problem is in the query. Generally, when you are writing subqueries, they must return only 1 result. So a subquery like the one voter_id:

select ..., (select sectio_threadrating.user_id from ...) as voter_id from ....

is invalid, because it can return more than one result. If you are sure it will always return one result, you can use the max() or min() aggregation function:

blahblah.extra(select = dict(myratings = '#####code above####',
                             voter_id = "SELECT max('section_threadrating'.'user_id') FROM 'section_threadrating' WHERE ('section_threadrating'.'content_object_id' = 'section_thread'.'id' AND 'section_threadrating'.'user_id' = '3') "))

This will make the subquery always return 1 result.

Removing that hard-code, what user_id are you expecting to retrieve here? Maybe you just can’t reduce to 1 user using only SQL.

👤augustomen

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