Support typed prepared statements

While datatypes are optional in prepared statements, not using them can results in type errors such as

function sum(text) does not exist

This is easily reproducible in any PSQL client

PREPARE my_query AS
SELECT SUM(CASE WHEN v = 'A' THEN $1 ELSE $2 END)
FROM (VALUES ('A'), ('B')) as q0(v);
-- ERROR: function sum(text) does not exist

But when I specify the types, it works

PREPARE my_query(int, int) AS
SELECT SUM(CASE WHEN v = 'A' THEN $1 ELSE $2 END)
FROM (VALUES ('A'), ('B')) as q0(v);

EXECUTE my_query(1,0);
-- 1

DEALLOCATE my_query;

asyncpg currently does not include types, which causes me to run into the sum(text) error. I'd expect it to either include types, or allow me to specify the types somehow.

Workaround:
Include a cast expression.
i.e.: $1::int or CAST($1 AS INT)

Full example

PREPARE my_query AS
SELECT SUM(CASE WHEN v = 'A' THEN $1::int ELSE $2::int END)
FROM (VALUES ('A'), ('B')) as q0(v);

Inizia riproducendo gli esempi di prepared statement in PostgreSQL tramite asyncpg e verifica come vengono gestiti i tipi dei parametri. Il lavoro è completato quando l’errore SUM(text) segnalato viene risolto supportando prepared statement tipizzati oppure fornendo ai chiamanti un modo per specificare i tipi dei parametri, con una copertura per la query mostrata.