/// if `expr` is a column name, returns the name
if `expr` is a column name, returns the name
if ` expr ` is a column name returns the name
fn as_col_name(expr: &Expr) -> Option<&str> {
    if let Expr::Column(inner) = expr {
        Some(inner.name.as_ref())
    } else {
        None
    }
}
fn as_col_name ( expr : & Expr ) -> Option < & str > { if let Expr :: Column ( inner ) = expr { Some ( inner . name . as_ref ( ) ) } else { None } }
if `expr` is a column name, returns the name
if ` expr ` is a column name returns the name
expr
&Expr