27 lines
6.1 KiB
HTML
27 lines
6.1 KiB
HTML
<!doctype html><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/5.1.0/github-markdown-dark.css><style>.markdown-body{box-sizing:border-box;min-width:200px;max-width:980px;margin:0 auto;padding:45px}@media(max-width:767px){.markdown-body{padding:15px}}</style><body class=markdown-body><a href=index>Index</a><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.
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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>This guide is not kind of guide which cover all cases.
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Just my little tricks when I work with SQL.<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.
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If you can, and you should, choose UUID type which can be sortable.<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, ...)
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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.
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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>It looks like this:<div class="highlight highlight-text-adblock"><pre>[Business] time, data -> convert to unix timestamp milliseconds -> [Database] int64</pre></div><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.
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Don't create index for every fields in table.
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Choose wisely!<p>For example, create index in MySQL:<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><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.<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><p>Need clarify why this happpen? Idk :(<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></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.
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Prefer <code>TEXT</code> if you don't care, just want to store something.<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, ...)<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><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></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>Use <a href=https://github.com/k1LoW/tbls>k1LoW/tbls</a> to grasp your database reality :)</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><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><a href=https://architecturenotes.co/things-you-should-know-about-databases/ rel=nofollow>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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