103 lines
6.7 KiB
HTML
103 lines
6.7 KiB
HTML
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<a href="index">Index</a>
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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>
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<p>Previously in my fresher software developer time, I rarely write SQL, I always use ORM to wrap SQL.
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But time past and too much abstraction bites me.
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So I decide to only write SQL from now as much as possible, no more ORM for me.
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But if there is any cool ORM for Go, I guess I try.</p>
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<p>This guide is not kind of guide which cover all cases.
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Just my little tricks when I work with SQL.</p>
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<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>
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<p>Use UUID instead.
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If you can, and you should, choose UUID type which can be sortable.</p>
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<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>
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<p>Stay away from all kind of database timestamp (MySQL timestmap, SQLite timestamp, ...)
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Just use int64 then pass the timestamp in service layer not database layer.</p>
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<p>Why? Because time and date and location are too much complex to handle.
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In my business, I use timestamp in milliseconds.
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Then I save timestamp as int64 value to database.
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Each time I get timestamp from database, I parse to time struct in Go with location or format I want.
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No more hassle!</p>
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<p>It looks like this:</p>
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<div class="highlight highlight-text-adblock"><pre>[Business] time, data -> convert to unix timestamp milliseconds -> [Database] int64</pre></div>
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<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>
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<p>You should use index for faster query, but not too much.
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Don't create index for every fields in table.
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Choose wisely!</p>
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<p>For example, create index in MySQL:</p>
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<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>`
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<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></div>
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<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>
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<p>If compare with field which can be NULL, remember to check NULL for safety.</p>
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<div class="highlight highlight-source-sql"><pre><span class="pl-c"><span class="pl-c">--</span> field_something can be NULL</span>
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<span class="pl-c"><span class="pl-c">--</span> Bad</span>
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<span class="pl-k">SELECT</span> <span class="pl-k">*</span>
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<span class="pl-k">FROM</span> table
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<span class="pl-k">WHERE</span> field_something <span class="pl-k">!=</span> <span class="pl-c1">1</span>
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<span class="pl-c"><span class="pl-c">--</span> Good</span>
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<span class="pl-k">SELECT</span> <span class="pl-k">*</span>
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<span class="pl-k">FROM</span> table
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<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>
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<p>Need clarify why this happpen? Idk :(</p>
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<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>
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<code>VARCHAR</code> or <code>TEXT</code>
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</h2>
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<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.
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Prefer <code>TEXT</code> if you don't care, just want to store something.</p>
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<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>
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<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>
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<ul>
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<li>
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<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>
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</li>
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<li>
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<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>
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</li>
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</ul>
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<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>
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<ul>
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<li>Use <a href="https://github.com/sqlfluff/sqlfluff">sqlfluff/sqlfluff</a> to check your SQL.</li>
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<li>Use <a href="https://github.com/k1LoW/tbls">k1LoW/tbls</a> to grasp your database reality :)</li>
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</ul>
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<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>
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<ul>
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<li><a href="https://use-the-index-luke.com/" rel="nofollow">Use The Index, Luke</a></li>
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<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>
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<li><a href="https://architecturenotes.co/things-you-should-know-about-databases/" rel="nofollow">Things You Should Know About Databases</a></li>
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</ul>
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<a href="mailto:hauvipapro+posts@gmail.com"
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>Feel free to ask me via email</a
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>
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<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>
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