golang mysql查询返回不定字段实现如下：
首先通过func (rs *Rows) Columns() ([]string, error)获取查询字段的slice，然后构造slice，将每次scan出来的值放进去，最后返回查询结果的map slice。

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/go-sql-driver/mysql"
)

func main() {
	conn, err := sql.Open("mysql", "root:psw@tcp(localhost:3306)/test?charset=utf8")
	if err != nil {
		fmt.Println("mysql connect error")
		return
	}

	defer conn.Close()
	rows, err := conn.Query("select * from user")
	if err != nil {
		fmt.Println("mysql query error", err.Error())
	}
	defer rows.Close()
	columns, err := rows.Columns()

	values := make([]sql.RawBytes, len(columns))
	scans := make([]interface{}, len(columns))

	for i := range values {
		scans[i] = &values[i]
	}

	var result []map[string]string
	for rows.Next() {
		_ = rows.Scan(scans...) 
		each := make(map[string]string)

		for i, col := range values {
			each[columns[i]] = string(col)
		}

		result = append(result, each)

	}

	fmt.Println(result)
}

同理查询单条也可以这样操作：

func main() {
	conn, err := sql.Open("mysql", "root:psw@tcp(localhost:3306)/test?charset=utf8")
	if err != nil {
		fmt.Println("mysql connect error", err.Error())
		return
	}

	defer conn.Close()

	columns := []string{"id", "name"}
	id := 1
	sql := fmt.Sprintf("select %s from user where id=%d", strings.Join(columns, ", "), id)
	row := conn.QueryRow(sql)

	values := make([][]byte, len(columns))
	scans := make([]interface{}, len(columns))

	for i := range values {
		scans[i] = &values[i]
	}

	if err := row.Scan(scans...); err != nil {
		fmt.Println("scan error", err.Error())
		return
	}

	var result = make(map[string]string)
	for key, val := range values {
		result[columns[key]] = string(val)
	}

	fmt.Println(result)
}