Subject: Re: Adaptation in psycopg3
To: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Cc: psycopg@postgresql.org
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From: listas <listas@soft-com.es>
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Date: Wed, 25 Nov 2020 19:00:21 +0100
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El 25/11/20 a las 15:45, Daniele Varrazzo escribió:
> On Wed, 25 Nov 2020 at 12:29, listas <listas@soft-com.es> wrote:
> 
>> After reading the docs i have a question about the parameters in the
>> 'in' clause.
>>
>> In psycopg2 i do:
>>
>>    params = (1,2,3,4)
>>    cursor.execute("select * from mytable where field1 in %s", (params,))
>>
>> or
>>
>>    params = ('black','red','green')
>>    cursor.execute("select * from mytable where field2 in %s", (params,))
>>
>> What will it be like in psycopg3, will it be the same?, will I have to
>> create a special adapter?
> 
> Hollo Oswaldo,
> 
> "IN" cannot be used, because it's a SQL construct, so "(1, 2, 3)" is
> not something that postgres will understand as a parameter.
> 
> You can use "= any (%s)" and pass a list. This is something you can do
> in psycopg2 too, and it's actually a better choice, because it works
> with empty lists too, unless `IN ()`, which is a syntax error for
> Postgres.
> 
> What you can do is:
> 
>      params = ['black','red','green']
>      cursor.execute("select * from mytable where field2 = any(%s)", (params,))
> 
> interesting fact: "= any" is what postgres really uses internally,
> even if you use the "IN ()" syntax:
> 
>      piro=# explain select * from mytable where myint in (1,2,3);
>                            QUERY PLAN
>      ---------------------------------------------------------
>      Seq Scan on mytable  (cost=0.00..45.06 rows=38 width=4)
>        Filter: (myint = ANY ('{1,2,3}'::integer[]))
>      (2 rows)
> 
>   -- Daniele
> 

Thank for your replies, I will use "=any(params list)" in psycopg3

The second question is: if psycopg3 is going to do the automatic cast of 
the types, will it be able to distinguish between a json and a list of 
values?.
Example:

data = ["a", "b", "c"]
idList = [4,7,2]

cursor.execute("update mytable set jsfield=%s where id = any(%s)", 
(data, idList))

What will be the correct syntax in this case?

Thanks,
--
Oswaldo Hernández