posts-go/docs/2022-07-31-sql.html

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<h1>
<a id="user-content-sql" class="anchor" aria-hidden="true" href="#sql"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>SQL
</h1>
<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>
<h2>
<a
id="user-content-stay-away-from-database-unique-id"
class="anchor"
aria-hidden="true"
href="#stay-away-from-database-unique-id"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Stay away from database unique id
</h2>
<p>
Use UUID instead. If you can, and you should, choose UUID type which can
be sortable.
</p>
<h2>
<a
id="user-content-stay-away-from-database-timestamp"
class="anchor"
aria-hidden="true"
href="#stay-away-from-database-timestamp"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Stay away from database timestamp
</h2>
<p>
Stay away from all kind of database timestamp (MySQL timestmap, 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 -&gt; convert to unix timestamp milliseconds -&gt; [Database] int64</pre
>
</div>
<h2>
<a
id="user-content-extra-field-for-extra-things"
class="anchor"
aria-hidden="true"
href="#extra-field-for-extra-things"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Extra field for extra things
</h2>
<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 also used for dumping request, response data.</p>
<h2>
<a
id="user-content-use-index"
class="anchor"
aria-hidden="true"
href="#use-index"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Use index!!!
</h2>
<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>
<h2>
<a
id="user-content-be-careful-with-null"
class="anchor"
aria-hidden="true"
href="#be-careful-with-null"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Be careful with NULL
</h2>
<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 happpen? Idk :(</p>
<h2>
<a
id="user-content-varchar-or-text"
class="anchor"
aria-hidden="true"
href="#varchar-or-text"
><span aria-hidden="true" class="octicon octicon-link"></span
></a>
<code>VARCHAR</code> or <code>TEXT</code>
</h2>
<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>
<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"
class="anchor"
aria-hidden="true"
href="#be-super-careful-when-migrate-update-database-on-production-and-online"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Be super careful when migrate, update database on production and
online!!!
</h2>
<p>
Plase 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>
<h2>
<a id="user-content-tools" class="anchor" aria-hidden="true" href="#tools"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Tools
</h2>
<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>
<h2>
<a
id="user-content-thanks"
class="anchor"
aria-hidden="true"
href="#thanks"
><span aria-hidden="true" class="octicon octicon-link"></span></a
>Thanks
</h2>
<ul>
<li>
<a href="https://use-the-index-luke.com/" rel="nofollow"
>Use The Index, Luke</a
>
</li>
<li>
<a
href="https://www.foxhound.systems/blog/essential-elements-of-high-performance-sql-indexes/"
rel="nofollow"
>Essential elements of high performance applications: SQL indexes</a
>
</li>
<li>
<a
href="https://architecturenotes.co/things-you-should-know-about-databases/"
rel="nofollow"
>Things You Should Know About Databases</a
>
</li>
<li>
<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
>
</li>
<li>
<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
>
</li>
<li>
<a
href="https://planetscale.com/blog/how-read-mysql-explains"
rel="nofollow"
>How to read MySQL EXPLAINs</a
>
</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>. Source
code is available on
<a href="https://github.com/haunt98/posts-go">GitHub</a>
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