Bun cannot scan float32 into float32 for MySQL FLOAT columns

[Re3os]

When using Bun with MySQL and a column of type FLOAT, the database/sql driver correctly returns a value of type float32. However, Bun fails to scan this value into a Go struct field of type float32 with the following error:
My code: https://github.com/WarhoopAll/Grimoire/blob/28c38ff89bdaa980ea1618c7e8802e3f991db6ca/app/model/character.go#L23

To Reproduce

Create a MySQL table with a FLOAT column:

CREATE TABLE characters (
    guid INT PRIMARY KEY,
    position_x FLOAT
);
INSERT INTO characters (guid, position_x) VALUES (1, -6279.93);

type DBCharacter struct {
 PositionX float32 `bun:"position_x"`
}

var character DBCharacter
err := bunDB.NewSelect().
    Model(&character).
    Where("guid = ?", 1).
    Scan(ctx)
if err != nil {
    log.Fatalf("Error: %v", err)
}

Fast sctipt for test

package main

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

  _ "github.com/go-sql-driver/mysql"
  "github.com/uptrace/bun"
  "github.com/uptrace/bun/dialect/mysqldialect"
)

func main() {
  dsn := "root:root@tcp(127.0.0.1:3306)/characters"


  sqlDB, err := sql.Open("mysql", dsn)
  if err != nil {
    log.Fatalf("Failed to open database: %v", err)
  }
  defer sqlDB.Close()

  // === go-sql-driver SQL-===
  var positionX interface{}
  err = sqlDB.QueryRow("SELECT position_x FROM characters WHERE guid = ?", 1).Scan(&positionX)
  if err != nil {
    log.Fatalf("Failed to execute query (database/sql): %v", err)
  }
  fmt.Printf("Raw value (database/sql): %v, Type: %T\n", positionX, positionX)

  // === Bun  mysqldialect ===
  bunDB := bun.NewDB(sqlDB, mysqldialect.New()) 
  defer bunDB.Close()

  var positionXWithBun float32
  err = bunDB.NewRaw("SELECT position_x FROM characters WHERE guid = ?", 1).
    Scan(context.Background(), &positionXWithBun)
  if err != nil {
    log.Fatalf("Failed to execute query (Bun): %v", err)
  }
  fmt.Printf("Value from Bun (mysqldialect): %f\n", positionXWithBun)
}

First go-sql-driver

Raw value (database/sql): -6279.927, Type: float32 - 32 type

Second mysqldialect

2024/12/17 23:07:05 Failed to execute query (Bun): sql: Scan error on column index 0, name "position_x": bun: can't scan -6279.93 (float32) into float32
Bun cannot scan float32 even in the float32 field

Change type 

var positionXWithBun float64

2024/12/17 23:40:32 Failed to execute query (Bun): sql: Scan error on column index 0, name "position_x": bun: can't scan -6279.93 (float32) into float64

okey check code

bun/schema/scan.go

Line 41 in 014b142

reflect.Float32: scanFloat64,

reflect.Float32: scanFloat64
there is no conversion of float32 to float64

add case

func scanFloat64(dest reflect.Value, src interface{}) error {
	switch src := src.(type) {
	case nil:
		dest.SetFloat(0)
		return nil
	case float32: // Safely convert float32 to float64
		dest.SetFloat(float64(src))
		return nil
	case float64:
		dest.SetFloat(src)
		return nil
	case []byte:
		f, err := strconv.ParseFloat(string(src), 64)
		if err != nil {
			return err
		}
		dest.SetFloat(f)
		return nil
	case string:
		f, err := strconv.ParseFloat(src, 64)
		if err != nil {
			return err
		}
		dest.SetFloat(f)
		return nil
	default:
		return scanError(dest.Type(), src)
	}
}

work fine:

Raw value (database/sql): -6279.927, Type: float32
Value from Bun (mysqldialect): -6279.930176

if now update 	var positionXWithBun float64

Raw value (database/sql): -6279.927, Type: float32
Value from Bun (mysqldialect): -6279.930176

work

mysql> SELECT CAST(position_x AS DOUBLE) AS precise_value FROM characters WHERE guid = 1;
+------------------+
| precise_value    |
+------------------+
| -6279.9267578125 |
+------------------+
1 row in set (0.02 sec)

mysql> SELECT position_x FROM characters WHERE guid = 1;
+------------+
| position_x |
+------------+
|   -6279.93 |
+------------+
1 row in set (0.01 sec)

mysql> SELECT VERSION();
+-----------+
| VERSION() |
+-----------+
| 8.0.40    |
+-----------+
1 row in set (0.01 sec)

mysql> DESCRIBE characters position_x;
+------------+-------+------+-----+---------+-------+
| Field      | Type  | Null | Key | Default | Extra |
+------------+-------+------+-----+---------+-------+
| position_x | float | NO   |     | 0       |       |
+------------+-------+------+-----+---------+-------+
1 row in set (0.03 sec)

go list -m github.com/go-sql-driver/mysql
github.com/go-sql-driver/mysql v1.8.1

go list -m github.com/uptrace/bun/dialect/mysqldialect
github.com/uptrace/bun/dialect/mysqldialect v1.2.6

Old issue
#993

[j2gg0s]

Thank you for your detailed issue.