diff --git a/base-blog-em/src/PostDetail.jsx b/base-blog-em/src/PostDetail.jsx
index 2af258fc..b295cd02 100644
--- a/base-blog-em/src/PostDetail.jsx
+++ b/base-blog-em/src/PostDetail.jsx
@@ -1,34 +1,46 @@
+import { useQuery, useMutation } from 'react-query'
+
 async function fetchComments(postId) {
-  const response = await fetch(
-    `https://jsonplaceholder.typicode.com/comments?postId=${postId}`
-  );
-  return response.json();
+  const response = await fetch(`https://jsonplaceholder.typicode.com/comments?postId=${postId}`)
+  return response.json()
 }
 
 async function deletePost(postId) {
-  const response = await fetch(
-    `https://jsonplaceholder.typicode.com/postId/${postId}`,
-    { method: "DELETE" }
-  );
-  return response.json();
+  const response = await fetch(`https://jsonplaceholder.typicode.com/postId/${postId}`, { method: 'DELETE' })
+  return response.json()
 }
 
 async function updatePost(postId) {
-  const response = await fetch(
-    `https://jsonplaceholder.typicode.com/postId/${postId}`,
-    { method: "PATCH", data: { title: "REACT QUERY FOREVER!!!!" } }
-  );
-  return response.json();
+  const response = await fetch(`https://jsonplaceholder.typicode.com/postId/${postId}`, {
+    method: 'PATCH',
+    data: { title: 'REACT QUERY FOREVER!!!!' }
+  })
+  return response.json()
 }
 
 export function PostDetail({ post }) {
-  // replace with useQuery
-  const data = [];
+  // 쿼리키를 배열로 만든다면 쿼리에 식별자를 추가하여 쿼리를 구분할 수 있음
+  // 비활성화된 쿼리는 캐시에서 제거되지 않음, 캐시 시간 이후에 가비지 컬렉터가 캐시에서 지움
+  // 비동기 함수를 화살표 함수로 만드는 것은 인수가 뭐든지간에 호출을 해야하기 때문에
+  const { data, isLoading, isError, error } = useQuery(['comments', post.id], () => fetchComments(post.id))
+
+  const deleteMutation = useMutation((postId) => deletePost(postId))
+  const updateMutation = useMutation((postId) => updatePost(postId))
+
+  if (isLoading) return <div>Loading...</div>
+  if (isError) return <div>{error.toString()}</div>
 
   return (
     <>
-      <h3 style={{ color: "blue" }}>{post.title}</h3>
-      <button>Delete</button> <button>Update title</button>
+      <h3 style={{ color: 'blue' }}>{post.title}</h3>
+      <button onClick={deleteMutation.mutate(post.id)}>Delete</button>
+      {deleteMutation.isError && <p style={{ color: 'red' }}>Error deleting the post</p>}
+      {deleteMutation.isLoading && <p style={{ color: 'purple' }}>deleting the post</p>}
+      {deleteMutation.isSuccess && <p style={{ color: 'green' }}>Post has (not) been deleted</p>}
+      <button onClick={updateMutation.mutate(post.id)}>Update title</button>
+      {updateMutation.isError && <p style={{ color: 'red' }}>Error updating the post</p>}
+      {updateMutation.isLoading && <p style={{ color: 'purple' }}>updating the post</p>}
+      {updateMutation.isSuccess && <p style={{ color: 'green' }}>Post has (not) been updated</p>}
       <p>{post.body}</p>
       <h4>Comments</h4>
       {data.map((comment) => (
@@ -37,5 +49,5 @@ export function PostDetail({ post }) {
         </li>
       ))}
     </>
-  );
+  )
 }
diff --git a/base-blog-em/src/Posts.jsx b/base-blog-em/src/Posts.jsx
index 9404d664..3c33b3aa 100644
--- a/base-blog-em/src/Posts.jsx
+++ b/base-blog-em/src/Posts.jsx
@@ -1,19 +1,34 @@
-import { useState } from 'react'
-import { useQuery } from 'react-query'
+import { useEffect, useState } from 'react'
+import { useQuery, useQueryClient } from 'react-query'
 import { PostDetail } from './PostDetail'
 const maxPostPage = 10
 
-async function fetchPosts() {
-  const response = await fetch('https://jsonplaceholder.typicode.com/posts?_limit=10&_page=0')
+async function fetchPosts(pageNum) {
+  const response = await fetch(`https://jsonplaceholder.typicode.com/posts?_limit=10&_page=${pageNum}`)
   return response.json()
 }
 
 export function Posts() {
-  const [currentPage, setCurrentPage] = useState(0)
+  const [currentPage, setCurrentPage] = useState(1)
   const [selectedPost, setSelectedPost] = useState(null)
 
+  const queryClient = useQueryClient()
+
+  useEffect(() => {
+    if (currentPage < maxPostPage) {
+      const nextPage = currentPage + 1
+      queryClient.prefetchQuery(['posts', nextPage], () => fetchPosts(nextPage), {
+        staleTime: 2000,
+        // 이전 페이지로 돌아갔을 때 캐시에 해당 지난 데이터가 있도록
+        keepPreviousData: true
+      })
+    }
+  }, [currentPage, queryClient])
+
   // replace with useQuery
-  const { data, isError, isLoading } = useQuery('posts', fetchPosts, { staleTime: 2000 })
+  const { data, isError, isLoading } = useQuery(['posts', currentPage], () => fetchPosts(currentPage), {
+    staleTime: 2000
+  })
   if (isLoading) return <div>Loading...</div>
   if (isError) return <div>something went wrong</div>
 
@@ -27,11 +42,11 @@ export function Posts() {
         ))}
       </ul>
       <div className="pages">
-        <button disabled onClick={() => {}}>
+        <button disabled={currentPage <= 1} onClick={() => setCurrentPage((prev) => prev - 1)}>
           Previous page
         </button>
-        <span>Page {currentPage + 1}</span>
-        <button disabled onClick={() => {}}>
+        <span>Page {currentPage}</span>
+        <button disabled={currentPage >= maxPostPage} onClick={() => setCurrentPage((prev) => prev + 1)}>
           Next page
         </button>
       </div>
diff --git a/base-blog-em/src/index.js b/base-blog-em/src/index.js
index ef2edf8e..09f66641 100644
--- a/base-blog-em/src/index.js
+++ b/base-blog-em/src/index.js
@@ -1,17 +1,12 @@
-import React from 'react';
-import ReactDOM from 'react-dom';
-import './index.css';
-import App from './App';
-import reportWebVitals from './reportWebVitals';
+import React from 'react'
+import ReactDOM from 'react-dom'
+import './index.css'
+import App from './App'
+import reportWebVitals from './reportWebVitals'
 
-ReactDOM.render(
-  <React.StrictMode>
-    <App />
-  </React.StrictMode>,
-  document.getElementById('root')
-);
+ReactDOM.render(<App />, document.getElementById('root'))
 
 // If you want to start measuring performance in your app, pass a function
 // to log results (for example: reportWebVitals(console.log))
 // or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
-reportWebVitals();
+reportWebVitals()