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From: Daniele Varrazzo <daniele.varrazzo@gmail.com>
Date: Wed, 25 Nov 2020 14:45:30 +0000
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Subject: Re: Adaptation in psycopg3
To: listas <listas@soft-com.es>
Cc: psycopg@postgresql.org
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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