16 lines
3.9 KiB
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16 lines
3.9 KiB
HTML
<!doctype html><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><link rel=preconnect href=https://fonts.googleapis.com><link rel=preconnect href=https://fonts.gstatic.com crossorigin><link href="https://fonts.googleapis.com/css2?family=Recursive:wght,CASL,MONO@300..800,0..1,0..1&display=swap" rel=stylesheet><link href=https://haunt98.github.io/iosevka_webfont/iosevka-term-ss08/iosevka-term-ss08.css rel=stylesheet><link rel=stylesheet href=styles.css><a href=index>Index</a><h1>SQL</h1><p>Previously in my fresher software developer time, I rarely write SQL, I always use ORM to wrap SQL.<br>But time past and too much abstraction bites me.<br>So I decide to only write SQL from now as much as possible, no more ORM for me.<br>But if there is any cool ORM for Go, I guess I try.<p>This guide is not kind of guide which cover all cases.<br>Just my little tricks when I work with SQL.<h2>Stay away from database unique id</h2><p>Use UUID instead.<br>If you can, and you should, choose UUID type which can be sortable.<h2>Stay away from database timestamp</h2><p>Stay away from all kind of database timestamp (MySQL timestmap, SQLite timestamp, ...)<br>Just use int64 then pass the timestamp in service layer not database layer.<p>Why? Because time and date and location are too much complex to handle.<br>In my business, I use timestamp in milliseconds.<br>Then I save timestamp as int64 value to database.<br>Each time I get timestamp from database, I parse to time struct in Go with location or format I want.<br>No more hassle!<p>It looks like this:<pre><code class=language-txt>[Business] time, data -> convert to unix timestamp milliseconds -> [Database] int64
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</code></pre><h2>Use index!!!</h2><p>You should use index for faster query, but not too much.<br>Don't create index for every fields in table.<br>Choose wisely!<p>For example, create index in MySQL:<pre><code class=language-sql>CREATE INDEX `idx_timestamp`
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ON `user_upload` (`timestamp`);
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</code></pre><h2>Be careful with NULL</h2><p>If compare with field which can be NULL, remember to check NULL for safety.<pre><code class=language-sql>-- field_something can be NULL
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-- Bad
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SELECT *
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FROM table
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WHERE field_something != 1
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-- Good
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SELECT *
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FROM table
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WHERE (field_something IS NULL OR field_something != 1)
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</code></pre><p>Need clarify why this happpen? Idk :(<h2><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.<br>Prefer <code>TEXT</code> if you don't care, just want to store something.<h2>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, ...)<ul><li><a href=https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-operations.html>For MySQL 5.7</a>, <a href=https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-limitations.html>Limitations</a><li><a href=https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-operations.html>For MySQL 8.0</a>, <a href=https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-limitations.html>Limitations</a></ul><h2>Tools</h2><ul><li>Use <a href=https://github.com/sqlfluff/sqlfluff>sqlfluff/sqlfluff</a> to check your SQL.<li>Use <a href=https://github.com/k1LoW/tbls>k1LoW/tbls</a> to grasp your database reality :)</ul><h2>Thanks</h2><ul><li><a href=https://use-the-index-luke.com/>Use The Index, Luke</a><li><a href=https://www.foxhound.systems/blog/essential-elements-of-high-performance-sql-indexes/>Essential elements of high performance applications: SQL indexes</a><li><a href=https://architecturenotes.co/things-you-should-know-about-databases/>Things You Should Know About Databases</a></ul><a href=mailto:hauvipapro+posts@gmail.com>Feel free to ask me via email</a>
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