Function avg

pub fn avg<'a, C>(col: C) -> Function<'a>
where
    C: Into<Column<'a>>,

Calculates the average value of a numeric column.

let query = Select::from_table("users").value(avg("age"));
let (sql, _) = Sqlite::build(query)?;
assert_eq!("SELECT AVG(`age`) FROM `users`", sql);