mismatched types; Rust type i32 (as SQL type INT4) is not compatible with SQL type INT8

create table item (
  id int8 primary key,
  name text not null,
  price numeric(10, 2),
  created_at timestamp not null default '2026-10-24 08:00:00',
  note text
);
-- 三行：price 依次是 9.90、NULL、3.50

  let r = sqlx::query_scalar::<_, i32>("select count(*) from item").fetch_one(&pool).await;
  println!("count(*) i32  -> {}", r.unwrap_err());
  let r = sqlx::query_scalar::<_, f64>("select price from item where id = 1").fetch_one(&pool).await;
  println!("numeric f64   -> {}", r.unwrap_err());
  let r = sqlx::query_scalar::<_, DateTime<Utc>>("select created_at from item where id = 1").fetch_one(&pool).await;
  println!("timestamp Utc -> {}", r.unwrap_err());

count(*) i32  -> error occurred while decoding column 0: mismatched types; Rust type `i32` (as SQL type `INT4`) is not compatible with SQL type `INT8`
numeric f64   -> error occurred while decoding column 0: mismatched types; Rust type `f64` (as SQL type `FLOAT8`) is not compatible with SQL type `NUMERIC`
timestamp Utc -> error occurred while decoding column 0: mismatched types; Rust type `chrono::datetime::DateTime<chrono::offset::utc::Utc>` (as SQL type `TIMESTAMPTZ`) is not compatible with SQL type `TIMESTAMP`

  let r = sqlx::query_scalar::<_, Option<f64>>("select price from item where id = 2").fetch_one(&pool).await;
  println!("NULL row only -> {:?}", r);
  let mut rows = sqlx::query_scalar::<_, Option<f64>>("select price from item order by price nulls first").fetch(&pool);
  while let Some(r) = rows.next().await {
    println!("stream        -> {}", r.map_or_else(|e| e.to_string(), |v| format!("{v:?}")));
  }

NULL row only -> Ok(None)
stream        -> None
stream        -> error occurred while decoding column 0: mismatched types; Rust type `core::option::Option<f64>` (as SQL type `FLOAT8`) is not compatible with SQL type `NUMERIC`
stream        -> error occurred while decoding column 0: mismatched types; Rust type `core::option::Option<f64>` (as SQL type `FLOAT8`) is not compatible with SQL type `NUMERIC`

        let value = self.try_get_raw(&index)?;

        if !value.is_null() {
            let ty = value.type_info();

            if !ty.is_null() && !T::compatible(&ty) {
                return Err(Error::ColumnDecode {
                    index: format!("{index:?}"),
                    source: mismatched_types::<Self::Database, T>(&ty),
                });
            }
        }

#[allow(dead_code)]
struct Stats {
  n: i32,
  price: Option<f64>,
}

// ...
  let s = sqlx::query_as!(Stats, r#"select count(*) as "n!", max(price) as price from item"#)
    .fetch_one(&pool)
    .await?;

error: SQLx feature `bigdecimal` required for type NUMERIC of column #2 ("price")
  --> src/bin/mismatched_macro.rs:10:11
   |
10 |   let s = sqlx::query_as!(Stats, r#"select count(*) as "n!", max(price) as price from item"#)
   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `$crate::sqlx_macros::expand_query` which comes from the expansion of the macro `sqlx::query_as` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `i32: From<i64>` is not satisfied
  --> src/bin/mismatched_macro.rs:10:11
   |
10 |   let s = sqlx::query_as!(Stats, r#"select count(*) as "n!", max(price) as price from item"#)
   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<i64>` is not implemented for `i32`
   |
...
   = note: required for `i64` to implement `Into<i32>`
...

  let n: i64 = sqlx::query_scalar("select count(*) from item").fetch_one(&pool).await?;
  let n32: i32 = sqlx::query_scalar("select count(*)::int4 from item").fetch_one(&pool).await?;
  let p: Vec<Option<f64>> = sqlx::query_scalar("select price::float8 from item order by id").fetch_all(&pool).await?;
  let s: Vec<Option<String>> = sqlx::query_scalar("select price::text from item order by id").fetch_all(&pool).await?;
  let t: NaiveDateTime = sqlx::query_scalar("select created_at from item where id = 1").fetch_one(&pool).await?;
  let tz: DateTime<Utc> = sqlx::query_scalar("select created_at at time zone 'UTC' from item where id = 1").fetch_one(&pool).await?;
  println!("i64 {n} | int4 {n32} | float8 {p:?} | text {s:?}");
  println!("NaiveDateTime {t} | at time zone 'UTC' {tz}");

i64 3 | int4 3 | float8 [Some(9.9), None, Some(3.5)] | text [Some("9.90"), None, Some("3.50")]
NaiveDateTime 2026-10-24 08:00:00 | at time zone 'UTC' 2026-10-24 08:00:00 UTC