Function join 

pub fn join<Sql, Arg>(
    sql: &mut Sql,
    typ: JoinType,
    table: &str,
    alias: Option<&str>,
)
where
    Sql: WriteSql<Arg>,

Starts a JOIN clause.

Example

let mut sql: SqlCommand<Void> = SqlCommand::default();
join(&mut sql, JoinType::Left, "user", Some("u"));

assert_eq!(sql.as_command(), "LEFT JOIN user AS u");