Rust: sqlite3 のデータを更新 (Update)

$ tree -L 2
.
├── Cargo.lock
├── Cargo.toml
├── src
│   └── main.rs
└── target
    └── debug

[package]
name = "sqlite3_update"
version = "0.1.0"
edition = "2018"

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

// --------------------------------------------------------------------
/*
    sqlite3_update/src/main.rs

                    Jul/23/2020
*/
// --------------------------------------------------------------------
use std::env;
use rusqlite::{params, Connection, Result};
use chrono::{Local, Date};

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

    let args: Vec<_> = env::args().collect();
    let file_sqlite3 = &args[1];
    let key_in = &args[2];
    let population_in = &args[3];

    eprintln!("{}",file_sqlite3);
    eprintln!("{}",key_in);
    eprintln!("{}",population_in);

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

    let conn = Connection::open(file_sqlite3).unwrap();

    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 + "'";

    eprintln!("{}",sql_str);

    conn.execute(&sql_str,params![],)?;

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

    Ok(())
}

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

$ cargo run /var/tmp/sqlite3/cities.db t0713 3512600
    Finished dev [unoptimized + debuginfo] target(s) in 1.24s
     Running `target/debug/sqlite3_update /var/tmp/sqlite3/cities.db t0713 3512600`
*** start ***
/var/tmp/sqlite3/cities.db
t0713
3512600
2020-07-23+09:00
update cities set population = 3512600, date_mod = '2020-07-23+09:00' where id = 't0713'
*** end ***