Macro bsql_update 

macro_rules! bsql_update {
    {
        let $bind:ident = $tname:ident { $($body:tt)+ } $(;)?
    } => { ... };
    {
        $tname:ident { $(
            $fname:ident $( : $value:expr )?
        ),* $(,)?
        }
    } => { ... };
    { @ $fname:ident } => { ... };
    { @ $fname:ident: $value:expr } => { ... };
}

Construct a RowUpdate or impl Bsql for some Row,

let _: RowUpdate = bsql_update! { Row {
    FIELD0: VALUE,
    FIELD1,
    // ..
} };

bsql_update! { let update = Row {
    FIELD0: VALUE,
    FIELD1,
    // ..
} };
let _: &dyn Bsql = &bsql!("UPDATE table SET " {update} "");