From 5cffdc47c72f640a778b2aaebbbaf9b24bcc327a Mon Sep 17 00:00:00 2001
From: Hau Nguyen <hauvipapro@gmail.com>
Date: Fri, 16 Jun 2023 02:31:21 +0700
Subject: [PATCH] feat: morr about index

---
 docs/2022-07-31-sql.html | 28 ++++++++++++++++++++++++++--
 posts/2022-07-31-sql.md  | 20 ++++++++++++++++++--
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/docs/2022-07-31-sql.html b/docs/2022-07-31-sql.html
index 7059365..b9485d3 100644
--- a/docs/2022-07-31-sql.html
+++ b/docs/2022-07-31-sql.html
@@ -126,8 +126,23 @@
     </p>
     <p>For example, create index in MySQL:</p>
     <div class="highlight highlight-source-sql">
-      <pre><span class="pl-k">CREATE</span> <span class="pl-k">INDEX</span> `<span class="pl-en">idx_timestamp</span>`
-    <span class="pl-k">ON</span> <span class="pl-s"><span class="pl-pds">`</span>user_upload<span class="pl-pds">`</span></span> (<span class="pl-s"><span class="pl-pds">`</span>timestamp<span class="pl-pds">`</span></span>);</pre>
+      <pre><span class="pl-k">CREATE</span> <span class="pl-k">INDEX</span> <span class="pl-en">idx_user_id</span>
+    <span class="pl-k">ON</span> user_upload (user_id);</pre>
+    </div>
+    <p>
+      If create index inside <code>CREATE TABLE</code>,
+      <a href="https://stackoverflow.com/a/1401615" rel="nofollow"
+        >prefer <code>INDEX</code> to <code>KEY</code></a
+      >:
+    </p>
+    <div class="highlight highlight-source-sql">
+      <pre><span class="pl-k">CREATE</span> <span class="pl-k">TABLE</span> <span class="pl-en">user_upload</span>
+(
+    id      <span class="pl-k">int</span>(<span class="pl-c1">11</span>) <span class="pl-k">NOT NULL</span>,
+    user_id <span class="pl-k">int</span>(<span class="pl-c1">11</span>) <span class="pl-k">NULL</span> DEFAULT <span class="pl-k">NULL</span>,
+    <span class="pl-k">PRIMARY KEY</span> (id),
+    INDEX idx_user_id (user_id)
+);</pre>
     </div>
     <p>Use <code>EXPLAIN</code> to check if index is used or not:</p>
     <ul>
@@ -188,6 +203,15 @@
       and make sure size of value will never hit the limit. Prefer
       <code>TEXT</code> if you don't care, just want to store something.
     </p>
+    <h2>
+      <a id="user-content-limit" class="anchor" aria-hidden="true" href="#limit"
+        ><span aria-hidden="true" class="octicon octicon-link"></span></a
+      ><code>LIMIT</code>
+    </h2>
+    <p>
+      Prefer <code>LIMIT 10 OFFSET 5</code> to <code>LIMIT 5, 10</code> to avoid
+      misunderstanding.
+    </p>
     <h2>
       <a
         id="user-content-be-super-careful-when-migrate-update-database-on-production-and-online"
diff --git a/posts/2022-07-31-sql.md b/posts/2022-07-31-sql.md
index 39733d8..7ec781a 100644
--- a/posts/2022-07-31-sql.md
+++ b/posts/2022-07-31-sql.md
@@ -49,8 +49,20 @@ Choose wisely!
 For example, create index in MySQL:
 
 ```sql
-CREATE INDEX `idx_timestamp`
-    ON `user_upload` (`timestamp`);
+CREATE INDEX idx_user_id
+    ON user_upload (user_id);
+```
+
+If create index inside `CREATE TABLE`, [prefer `INDEX` to `KEY`](https://stackoverflow.com/a/1401615):
+
+```sql
+CREATE TABLE user_upload
+(
+    id      int(11) NOT NULL,
+    user_id int(11) NULL DEFAULT NULL,
+    PRIMARY KEY (id),
+    INDEX idx_user_id (user_id)
+);
 ```
 
 Use `EXPLAIN` to check if index is used or not:
@@ -83,6 +95,10 @@ Need clarify why this happpen? Idk :(
 Prefer `VARCHAR` if you need to query and of course use index, and make sure size of value will never hit the limit.
 Prefer `TEXT` if you don't care, just want to store something.
 
+## `LIMIT`
+
+Prefer `LIMIT 10 OFFSET 5` to `LIMIT 5, 10` to avoid misunderstanding.
+
 ## Be super careful when migrate, update database on production and online!!!
 
 Plase read docs about online ddl operations before do anything online (keep database running the same time update it, for example create index, ...)