Function total 

pub fn total<'a, V, E>(
    expr: E,
) -> SQLExpr<'a, V, <V::DialectMarker as DialectTypes>::Double, NonNull, Agg>
where
    V: SQLParam + 'a,
    V::DialectMarker: SQLiteAggregateSupport,
    E: Expr<'a, V>,
    E::SQLType: Numeric,

TOTAL - sums numeric values, returning 0.0 for empty sets (SQLite).

Unlike SUM, which returns NULL for an empty result set, TOTAL always returns a floating-point value (0.0 for empty sets).

Example

use drizzle_core::expr::total;

// SELECT TOTAL(orders.amount)
let total_amount = total(orders.amount);