GraphQL is a query language for your API that was developed by Facebook. It provides an alternative to REST APIs, and allows the client to request specific data from the server rather than getting a fixed set of data with each request.

One key difference between GraphQL and REST APIs is that in a GraphQL API, the client can specify exactly which fields it wants to retrieve in the query, rather than getting a fixed set of data with each endpoint. This allows the client to request only the data it needs, rather than getting more data than it needs and filtering it on the client side.

+--------+          +------------+          +------------+
|        |  ------> |            |  ------> |            |
| Client |          |   Server   |          |   Client   |
|        |  <------ |            |  <------ |            |
+--------+          +------------+          +------------+
  |  GraphQL        | GraphQL        |  filtered &
  |  query          |   response     |  requested data
  |                 |                |
  +-----------------+----------------+

1. The client sends a GraphQL query to the server, specifying the specific data it wants to retrieve.
2. The server processes the query and returns a response with the requested data.
3. The client receives the response and can use the data to update its state or display it to the user.

Here is an example of a GraphQL query in Go that uses the GitHub API to retrieve the name and description of a repository:

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package main

import (
	"bytes"
	"context"
	"fmt"
	"io/ioutil"
	"net/http"

	"github.com/shurcooL/githubv4"
)

func main() {
	src := oauth2.StaticTokenSource(
		&oauth2.Token{AccessToken: "<YOUR_ACCESS_TOKEN>"},
	)
	httpClient := oauth2.NewClient(context.Background(), src)
	client := githubv4.NewClient(httpClient)

	// Define the GraphQL query
	var query struct {
		Repository struct {
			Name        githubv4.String
			Description githubv4.String
		} `graphql:"repository(owner: $owner, name: $name)"`
	}
	variables := map[string]interface{}{
		"owner": githubv4.String("<OWNER>"),
		"name":  githubv4.String("<REPO_NAME>"),
	}

	// Execute the query
	err := client.Query(context.Background(), &query, variables)
	if err != nil {
		fmt.Println(err)
		return
	}

	// Print the results
	fmt.Println(query.Repository.Name)
	fmt.Println(query.Repository.Description)
}

In this example, the Repository field in the query specifies the data that the client wants to retrieve, and the owner and name variables are used to specify the repository that the client wants to query. The client.Query function is used to execute the query and retrieve the data from the server.