Implement transfer creation

postgres/numeric/numeric.go

@@ -83,6 +83,10 @@ func (n Numeric) Sub(other Numeric) Numeric {
 	panic("Cannot subtract with different exponents")
 }
 
+func (n Numeric) Neg() Numeric {
+	return Numeric{pgtype.Numeric{Exp: n.Exp, Int: big.NewInt(-1 * n.Int.Int64()), Status: n.Status}}
+}
+
 func (n Numeric) Add(other Numeric) Numeric {
 	left := n
 	right := other