Function row_number 

pub fn row_number() -> row_number

Number of th current row within its partition

Returns the number of the current row within its partition, counting from 1.

This function must be used as window function. You need to call at least one of the methods WindowExpressionMethods from to use this function in your SELECT clause. It cannot be used outside of SELECT clauses.

let res = posts
    .select((title, user_id, row_number().partition_by(user_id)))
    .load::<(String, i32, i64)>(connection)?;
let expected = vec![
    ("My first post".to_owned(), 1, 1),
    ("About Rust".into(), 1, 2),
    ("My first post too".into(), 2, 1),
];
assert_eq!(expected, res);