Result type for single column query

[zhus]

The result type of conn.query("select 2+2, 3+3 from RDB$DATABASE", ())?; is Vec<(i32,i32)>.
How to describe single column result conn.query("select 1+1 from RDB$DATABASE", ())?;?
Not Vec<i32> nor Vec<(i32)> not compiled with

error[E0277]: the trait bound `i32: FromRow` is not satisfied
  --> src\main.rs:18:33
   |
18 |     let rows: Vec<(i32)> = conn.query("select 1+1 from RDB$DATABASE", ())?;
   |                                 ^^^^^ the trait `FromRow` is not implemented for `i32`
   |
   = help: the following other types implement trait `FromRow`:
             ()
             (A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
             (G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z)
           and 20 others
note: required by a bound in `query`
  --> C:\Projects\rsfbclient\src\query.rs:47:12
   |
47 |         R: FromRow + 'static,
   |            ^^^^^^^ required by this bound in `query`

[fernandobatels]

(i32) is not a tuple, you need use a extra , when you have a single column to force a tuple:

let rows: Vec<(i32,)> = conn.query("select 1+1 from RDB$DATABASE", ())?;

You can also use the query_first if you only need one row:

let (sum,): (i32,) = conn.query_first("select 1+1 from RDB$DATABASE", ())?.unwrap();

[zhus]

i see, thanks!