pub fn lead<'a, V, E>( expr: E, ) -> WindowFnExpr<'a, V, <E as Expr<'a, V>>::SQLType, Null>where V: SQLParam + 'a, E: Expr<'a, V>,
LEAD(expr) — value of expr from the next row.
Returns the same type as expr, always nullable (no next row → NULL).