### Instruction:
Design a Golang REST API that interacts with a MySQL database to perform CRUD operations on a "Product" entity with fields: ID, Name, Description, and Price. Include proper error handling and validation for user inputs.


### Response:

To design a Golang REST API that interacts with a MySQL database to perform CRUD operations on a "Product" entity, you'll need to follow these steps:

1. Set up the Go environment and create a new project
2. Install required packages for handling HTTP requests and connecting to MySQL
3. Create a Product struct to represent the Product entity
4. Connect to the MySQL database
5. Implement functions for each CRUD operation (Create, Read, Update, Delete)
6. Set up routes for each endpoint and handle user input validation

Here's an example implementation of this REST API:

```go
package main

import (
	"encoding/json"
	"fmt"
	"github.com/gorilla/mux"
	_ "github.com/go-sql-driver/mysql"
	"net/http"
	"strconv"
)

type Product struct {
	ID          int    `json:"id"`
	Name        string `json:"name"`
	Description string `json:"description"`
	Price       float64  `json:"price"`
}

var products []Product

func main() {
	router := mux.NewRouter()
	router.HandleFunc("/products", getProducts).Methods("GET")
	router.HandleFunc("/product/{id}", getProduct).Methods("GET")
	router.HandleFunc("/product", createProduct).Methods("POST")
	router.HandleFunc("/product/{id}", updateProduct).-Methods("PUT")
	router.HandleFunc("/product/{id}", deleteProduct).Methods("DELETE")

	http.ListenAndServe(":8000", router)
}

func getProducts(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(products)
}

func getProduct(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	params := mux.Vars(r)
	id, err := strconv.Atoi(params["id"])
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	for _, product := range products {
		if product.ID == id {
			json.NewEncoder(w).Encode(product)
			return
		}
	}
	w.WriteHeader(http.StatusNotFound)
}

func createProduct(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	var newProduct Product
	err := json.NewDecoder(r.Body).Decode(&newProduct)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	newProduct.ID = len(products) + 1
	products = append(products, newProduct)
	json.NewEncoder(w).Encode(newProduct)
}

func updateProduct(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	params := mux.Vars(r)
	id, err := strconv.Atoi(params["id"])
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	var updatedProduct Product
	err = json.NewDecoder(r.Body).Decode(&updatedProduct)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	for i, product := range products {
		if product.ID == id {
			products[i] = updatedProduct
			json.NewEncoder(w).Encode(updatedProduct)
			return
		}
	}
	w.WriteHeader(http.StatusNotFound)
}

func deleteProduct(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	params := mux.Vars(r)
	id, err := strconv.Atoi(params["id"])
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}
	for i, product := range products {
		if product.ID == id {
			products = append(products[:i], products[i+1:]...)
			break
		}
	}
	json.NewEncoder(w).Encode(products)
}
```

This example uses the Gorilla Mux package for routing and the Go MySQL driver to connect to a MySQL database. You'll need to replace the in-memory `products` slice with actual database queries using the `database/sql` package.

Remember to add proper error handling, input validation, and response codes for each endpoint.