JSON 对象列上的 PostgreSQL JOIN

Question

I'm supposed to join 3 different tables on postgres:

• lote_item (on which I have some books id's)
• lote_item_log (on which I have a column "attributes", with a JSON object such as {"aluno_id": "2823", "aluno_email": "someemail@outlook.com", "aluno_unidade": 174, "livro_codigo": "XOZK-0NOYP0Z1EMJ"} ) - Obs.: Some values on aluno_unidade are null

and finally

• company (on which I have every school name for every aluno_unidade. Ex: aluno_unidade = 174 ==> nome_fantasia = mySchoolName ).

Joining the first two tables was easy, since lote_item_log has a foreign key which I could match like this:

SELECT * FROM lote_item JOIN lote_item_log ON lote_item.id = lote_item_log.lote_item_id

Now, I need to get the School Name , contained on table company , with the aluno_unidade ID from table lote_item_log .

My current query is:

        SELECT 
            *
        FROM 
            lote_item
        JOIN
            lote_item_log
        ON
            lote_item.id = lote_item_log.lote_item_id
        JOIN
            company
        ON
            (
                SELECT
                    JSON_EXTRACT_PATH_TEXT(attributes, 'aluno_unidade')::int
                FROM
                    lote_item_log
                WHERE
                    operation_id = 6
            ) = company.senior_id
        WHERE 
            item_id = {book_id};

operation_id determines which school is active.

ERROR I'M GETTING:

sqlalchemy.exc.ProgrammingError: (psycopg2.errors.CardinalityViolation) more than one row returned by a subquery used as an expression

I tried LIMIT 1, but then I got just an empty array.

What I need is:

lote_item.created_at | lote_item.updated_at | lote_item.item_id | uuid | aluno_email | c014_id | nome_fantasia | cnpj | is_franchise | is_active
         somedate    |     somedate         |   some_item_id    | XJW4 | someemail@a | some_id | SCHOOL NAME   | cnpj |    t       |      t       

Answer 1

I got it.

Not sure it's the best way, but worked...

        SELECT 
            *
        FROM 
            lote_item
        JOIN
            lote_item_log
        ON
            lote_item.id = lote_item_log.lote_item_id
        JOIN
            company
        ON
            JSON_EXTRACT_PATH_TEXT(attributes, 'aluno_unidade')::int = company.senior_id
        WHERE 
            item_id = {book_id};