Sum系列方法

求和数据可以使用Sum, SumInt, Sums 和 SumsInt 四个方法，Sums系列方法的参数为struct的指针并且成为查询条件。

• Sum 求某个字段的和，返回float64

type SumStruct struct {
    Id int64
    Money int
    Rate float32
}
ss := new(SumStruct)
total, err := engine.Where("id >?", 1).Sum(ss, "money")
fmt.Printf("money is %d", int(total))

• SumInt 求某个字段的和，返回int64

type SumStruct struct {
    Id int64
    Money int
    Rate float32
}
ss := new(SumStruct)
total, err := engine.Where("id >?", 1).SumInt(ss, "money")
fmt.Printf("money is %d", total)

• Sums 求某几个字段的和， 返回float64的Slice

ss := new(SumStruct)
totals, err := engine.Where("id >?", 1).Sums(ss, "money", "rate")
fmt.Printf("money is %d, rate is %.2f", int(total[0]), total[1])

• SumsInt 求某几个字段的和， 返回int64的Slice

ss := new(SumStruct)
totals, err := engine.Where("id >?", 1).SumsInt(ss, "money")
fmt.Printf("money is %d", total[0])