Demonstration of float scan bug in github.com/go-sql-driver/mysql

float_bug.go

package main

import (
	"database/sql"
	"fmt"
	"log"

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

func main() {
	db, err := sql.Open("mysql", "root:@tcp(localhost:3306)/float_bug")
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println("With no placeholders:")
	printRows(db.Query("SELECT id, lat, lon FROM lat_lons WHERE id IN(1, 2)"))
	fmt.Println("\nWith placeholder:")
	printRows(db.Query("SELECT id, lat, lon FROM lat_lons WHERE id IN(?, ?)", 1, 2))

}

func printRows(rows *sql.Rows, err error) {
	if err != nil {
		log.Fatal(err)
	}

	var (
		id       int
		lat, lon *float64
	)

	for rows.Next() {
		if err = rows.Scan(&id, &lat, &lon); err != nil {
			log.Fatal(err)
		}
		fmt.Println(id, *lat, *lon)
	}
	rows.Close()
}

float_bug.sql

CREATE TABLE `lat_lons` (
  `id` int,
  `lat` float,
  `lon` float
);
INSERT INTO `lat_lons` VALUES (1, 33.9534, -117.396);
INSERT INTO `lat_lons` VALUES (2, 35.7942, -115.401);

output.txt

With no placeholders:
1 33.9534 -117.396
2 35.7942 -115.401

With placeholder:
1 33.953399658203125 -117.39600372314453
2 35.7942008972168 -115.4010009765625