Rust: PostgreSQL のデータを更新 (Update)

[package]
name = "postgres_update"
version = "0.1.0"
edition = "2018"

[dependencies]
postgres = "*"
chrono = "0.4"

// --------------------------------------------------------------------
/*
    postgres_update/src/main.rs

                    Jul/24/2020
*/
// --------------------------------------------------------------------
use std::env;
use postgres::{Client, NoTls, Error};
use chrono::{Local, Date};

// --------------------------------------------------------------------
fn main() -> Result<(), Error> {
    eprintln!("*** start ***");

    let args: Vec<_> = env::args().collect();
    let key_in = &args[1];
    let population_in = &args[2];
    eprintln!("{}",key_in);
    eprintln!("{}",population_in);

    let mut client = Client::connect("postgresql://scott:tiger123@localhost/city", NoTls)?;

    let date_mod: Date<Local> = Local::today();
    println!("{}", date_mod);

    let sql_str = "update cities set population = ".to_owned()
        + population_in + &", date_mod = '".to_owned()
        + &date_mod.to_string()
        + &"' where id = '".to_owned() + key_in + "'";

    client.batch_execute(&sql_str)?;

    eprintln!("*** end ***");
    Ok(())
}

// --------------------------------------------------------------------

cargo run t3462 7621300