464 lines
15 KiB
HTML
464 lines
15 KiB
HTML
<!doctype html>
|
||
<html>
|
||
<head>
|
||
<meta charset="utf-8" />
|
||
<meta name="viewport" content="width=device-width, initial-scale=1" />
|
||
<link
|
||
rel="stylesheet"
|
||
href="https://cdnjs.cloudflare.com/ajax/libs/github-markdown-css/5.6.1/github-markdown.min.css"
|
||
/>
|
||
<title>haunt98 posts</title>
|
||
</head>
|
||
<style>
|
||
.markdown-body {
|
||
box-sizing: border-box;
|
||
min-width: 200px;
|
||
max-width: 980px;
|
||
margin: 0 auto;
|
||
padding: 45px;
|
||
font-family:
|
||
Shantell Sans Normal,
|
||
Rec Mono Casual,
|
||
SF Pro,
|
||
Inter,
|
||
sans-serif;
|
||
font-weight: 500;
|
||
}
|
||
|
||
.markdown-body pre {
|
||
font-family:
|
||
Berkeley Mono,
|
||
IBM Plex Mono,
|
||
SF Mono,
|
||
Jetbrains Mono,
|
||
monospace;
|
||
}
|
||
|
||
@media (max-width: 767px) {
|
||
.markdown-body {
|
||
padding: 15px;
|
||
}
|
||
}
|
||
</style>
|
||
<body class="markdown-body">
|
||
<h2>
|
||
<a href="index.html"><code>~</code></a>
|
||
</h2>
|
||
<div class="markdown-heading">
|
||
<h1 class="heading-element">SQL</h1>
|
||
<a
|
||
id="user-content-sql"
|
||
class="anchor"
|
||
aria-label="Permalink: SQL"
|
||
href="#sql"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Previously in my fresher software developer time, I rarely write SQL, I
|
||
always use ORM to wrap SQL. But time past and too much abstraction bites
|
||
me. So I decide to only write SQL from now as much as possible, no more
|
||
ORM for me. But if there is any cool ORM for Go, I guess I try.
|
||
</p>
|
||
<p>
|
||
This guide is not kind of guide which cover all cases. Just my little
|
||
tricks when I work with SQL.
|
||
</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Stay away from database unique id</h2>
|
||
<a
|
||
id="user-content-stay-away-from-database-unique-id"
|
||
class="anchor"
|
||
aria-label="Permalink: Stay away from database unique id"
|
||
href="#stay-away-from-database-unique-id"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Use UUID instead. If you can, and you should, choose UUID type which can
|
||
be sortable.
|
||
</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Stay away from database timestamp</h2>
|
||
<a
|
||
id="user-content-stay-away-from-database-timestamp"
|
||
class="anchor"
|
||
aria-label="Permalink: Stay away from database timestamp"
|
||
href="#stay-away-from-database-timestamp"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Stay away from all kind of database timestamp (MySQL timestamp, SQLite
|
||
timestamp, ...) Just use int64 then pass the timestamp in service layer
|
||
not database layer.
|
||
</p>
|
||
<p>
|
||
Why? Because time and date and location are too much complex to handle. In
|
||
my business, I use timestamp in milliseconds. Then I save timestamp as
|
||
int64 value to database. Each time I get timestamp from database, I parse
|
||
to time struct in Go with location or format I want. No more hassle!
|
||
</p>
|
||
<p>It looks like this:</p>
|
||
<div class="highlight highlight-text-adblock">
|
||
<pre>
|
||
[Business] time, data -> convert to unix timestamp milliseconds -> [Database] int64</pre
|
||
>
|
||
</div>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Extra field for extra things</h2>
|
||
<a
|
||
id="user-content-extra-field-for-extra-things"
|
||
class="anchor"
|
||
aria-label="Permalink: Extra field for extra things"
|
||
href="#extra-field-for-extra-things"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Create new column in database is scary, so I suggest avoid it if you can.
|
||
How to avoid, first design table with extra field. It is black hole, put
|
||
everything in there if you want.
|
||
</p>
|
||
<p>I always use MySQL json data type for extra field.</p>
|
||
<p>JSON data type is also useful for dumping request, response data.</p>
|
||
<ul>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/5.7/en/json.html"
|
||
rel="nofollow"
|
||
>For MySQL 5.7</a
|
||
>
|
||
</li>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/8.0/en/json.html"
|
||
rel="nofollow"
|
||
>For MySQL 8.0</a
|
||
>
|
||
</li>
|
||
</ul>
|
||
<p>
|
||
Use <code>JSON_EXTRACT(col, '$.key') IS NULL</code> to check json field
|
||
exist or not.
|
||
</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Use index!!!</h2>
|
||
<a
|
||
id="user-content-use-index"
|
||
class="anchor"
|
||
aria-label="Permalink: Use index!!!"
|
||
href="#use-index"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
You should use index for faster query, but not too much. Don't create
|
||
index for every fields in table. Choose wisely!
|
||
</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_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>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/5.7/en/explain-output.html"
|
||
rel="nofollow"
|
||
>For MySQL 5.7</a
|
||
>
|
||
</li>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/8.0/en/explain-output.html"
|
||
rel="nofollow"
|
||
>For MySQL 8.0</a
|
||
>
|
||
</li>
|
||
</ul>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Be careful with UTF-8</h2>
|
||
<a
|
||
id="user-content-be-careful-with-utf-8"
|
||
class="anchor"
|
||
aria-label="Permalink: Be careful with UTF-8"
|
||
href="#be-careful-with-utf-8"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>TLDR with MySQL:</p>
|
||
<div class="highlight highlight-source-sql">
|
||
<pre><span class="pl-k">CREATE</span> <span class="pl-k">TABLE</span> <span class="pl-en">ekyc_approved</span>
|
||
(
|
||
id <span class="pl-k">varchar</span>(<span class="pl-c1">30</span>) <span class="pl-k">NOT NULL</span>,
|
||
<span class="pl-k">PRIMARY KEY</span> (id),
|
||
) ENGINE <span class="pl-k">=</span> InnoDB
|
||
DEFAULT CHARSET <span class="pl-k">=</span> utf8mb4;</pre>
|
||
</div>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Be careful with NULL</h2>
|
||
<a
|
||
id="user-content-be-careful-with-null"
|
||
class="anchor"
|
||
aria-label="Permalink: Be careful with NULL"
|
||
href="#be-careful-with-null"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
If compare with field which can be NULL, remember to check NULL for
|
||
safety.
|
||
</p>
|
||
<div class="highlight highlight-source-sql">
|
||
<pre><span class="pl-c"><span class="pl-c">--</span> field_something can be NULL</span>
|
||
|
||
<span class="pl-c"><span class="pl-c">--</span> Bad</span>
|
||
<span class="pl-k">SELECT</span> <span class="pl-k">*</span>
|
||
<span class="pl-k">FROM</span> table
|
||
<span class="pl-k">WHERE</span> field_something <span class="pl-k">!=</span> <span class="pl-c1">1</span>
|
||
|
||
<span class="pl-c"><span class="pl-c">--</span> Good</span>
|
||
<span class="pl-k">SELECT</span> <span class="pl-k">*</span>
|
||
<span class="pl-k">FROM</span> table
|
||
<span class="pl-k">WHERE</span> (field_something IS <span class="pl-k">NULL</span> <span class="pl-k">OR</span> field_something <span class="pl-k">!=</span> <span class="pl-c1">1</span>)</pre>
|
||
</div>
|
||
<p>Need clarify why this happen? Idk :(</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element"><code>VARCHAR</code> or <code>TEXT</code></h2>
|
||
<a
|
||
id="user-content-varchar-or-text"
|
||
class="anchor"
|
||
aria-label="Permalink: VARCHAR or TEXT"
|
||
href="#varchar-or-text"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Prefer <code>VARCHAR</code> if you need to query and of course use index,
|
||
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>
|
||
<p>If you need to store UUID, use <code>VARCHAR(255)</code>.</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element"><code>LIMIT</code></h2>
|
||
<a
|
||
id="user-content-limit"
|
||
class="anchor"
|
||
aria-label="Permalink: LIMIT"
|
||
href="#limit"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Prefer <code>LIMIT 10 OFFSET 5</code> to <code>LIMIT 5, 10</code> to avoid
|
||
misunderstanding.
|
||
</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">
|
||
Be super careful when migrate, update database on production and
|
||
online!!!
|
||
</h2>
|
||
<a
|
||
id="user-content-be-super-careful-when-migrate-update-database-on-production-and-online"
|
||
class="anchor"
|
||
aria-label="Permalink: Be super careful when migrate, update database on production and online!!!"
|
||
href="#be-super-careful-when-migrate-update-database-on-production-and-online"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>
|
||
Please read docs about online ddl operations before do anything online
|
||
(keep database running the same time update it, for example create index,
|
||
...)
|
||
</p>
|
||
<ul>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-operations.html"
|
||
rel="nofollow"
|
||
>For MySQL 5.7</a
|
||
>,
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-limitations.html"
|
||
rel="nofollow"
|
||
>Limitations</a
|
||
>
|
||
</li>
|
||
<li>
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-operations.html"
|
||
rel="nofollow"
|
||
>For MySQL 8.0</a
|
||
>,
|
||
<a
|
||
href="https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-limitations.html"
|
||
rel="nofollow"
|
||
>Limitations</a
|
||
>
|
||
</li>
|
||
</ul>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Heathcheck</h2>
|
||
<a
|
||
id="user-content-heathcheck"
|
||
class="anchor"
|
||
aria-label="Permalink: Heathcheck"
|
||
href="#heathcheck"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<p>Use <code>SELECT 1</code> to check if database failed yet.</p>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Tools</h2>
|
||
<a
|
||
id="user-content-tools"
|
||
class="anchor"
|
||
aria-label="Permalink: Tools"
|
||
href="#tools"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<ul>
|
||
<li>
|
||
Use
|
||
<a href="https://github.com/sqlfluff/sqlfluff">sqlfluff/sqlfluff</a> to
|
||
check your SQL.
|
||
</li>
|
||
<li>
|
||
Use <a href="https://github.com/k1LoW/tbls">k1LoW/tbls</a> to grasp your
|
||
database reality :)
|
||
</li>
|
||
</ul>
|
||
<div class="markdown-heading">
|
||
<h2 class="heading-element">Thanks</h2>
|
||
<a
|
||
id="user-content-thanks"
|
||
class="anchor"
|
||
aria-label="Permalink: Thanks"
|
||
href="#thanks"
|
||
><span aria-hidden="true" class="octicon octicon-link"></span
|
||
></a>
|
||
</div>
|
||
<ul>
|
||
<li>
|
||
<p>
|
||
<a href="https://use-the-index-luke.com/" rel="nofollow"
|
||
>Use The Index, Luke</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a
|
||
href="https://kevin.burke.dev/kevin/reddits-database-has-two-tables/"
|
||
rel="nofollow"
|
||
>Reddit’s database has two tables</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a
|
||
href="https://shekhargulati.com/2022/07/08/my-notes-on-gitlabs-postgres-schema-design/"
|
||
rel="nofollow"
|
||
>My Notes on GitLab Postgres Schema Design</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a
|
||
href="https://shekhargulati.com/2022/01/08/when-to-use-json-data-type-in-database-schema-design/"
|
||
rel="nofollow"
|
||
>When to use JSON data type in database schema design?</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a
|
||
href="https://planetscale.com/blog/how-read-mysql-explains"
|
||
rel="nofollow"
|
||
>How to read MySQL EXPLAINs</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a
|
||
href="https://brandur.org/fragments/database-health-check"
|
||
rel="nofollow"
|
||
>Honest health checks that hit the database</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://www.grouparoo.com/blog/varchar-191" rel="nofollow"
|
||
>Why are database columns 191 characters?</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/a/43056611" rel="nofollow"
|
||
>Store UUID v4 in MySQL</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/a/4849030" rel="nofollow"
|
||
>Difference between text and varchar (character varying)</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/q/33889922" rel="nofollow"
|
||
>How to get the number of total results when there is LIMIT in
|
||
query?</a
|
||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/q/28888375" rel="nofollow"
|
||
>Run a query with a LIMIT/OFFSET and also get the total number of
|
||
rows</a
|
||
>
|
||
</p>
|
||
</li>
|
||
</ul>
|
||
|
||
<div>
|
||
Feel free to ask me via
|
||
<a href="mailto:hauvipapro+posts@gmail.com">email</a> or
|
||
<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>.
|
||
<br />Source code is available on
|
||
<a href="https://github.com/haunt98/posts-go">GitHub</a>
|
||
<a href="https://codeberg.org/yoshie/posts-go">Codeberg</a>
|
||
<a href="https://git.sr.ht/~youngyoshie/posts-go">sourcehut</a>
|
||
<a href="https://gitea.treehouse.systems/yoshie/posts-go">Treehouse</a>
|
||
<a href="https://gitlab.com/youngyoshie/posts-go">GitLab</a>
|
||
</div>
|
||
</body>
|
||
</html>
|