main.go

package main

import (
	"database/sql"
	"fmt"

	_ "github.com/go-sql-driver/mysql"
)

func must(err error) {
	if err != nil {
		panic(err)
	}
}

func main() {
	var (
		v1, v2 any
		db     *sql.DB
	)

	db, err := sql.Open("mysql", "root@tcp(127.0.0.1:3306)/test")
	must(err)

	err = db.QueryRow(`select sum(JSON_EXTRACT(name, '$.hoge1.fuga1')) as piyo from users`).Scan(&v1)

	fmt.Printf("%T, %v, %v\n", v1, v1, err) // output: 100000, nil

	err = db.QueryRow(`
  select sum(JSON_EXTRACT(name, '$.hoge2.fuga2')) as piyo from users`).Scan(&v2)

	fmt.Printf("%T, %v, %v\n", v1, v2, err) // output: 0, Scan error on column index 0, name "piyo": converting driver.Value type float64 ("1e+06") to a int64: invalid syntax
}