464 lines
15 KiB
HTML
464 lines
15 KiB
HTML
<!doctype html>
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<html>
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<head>
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<meta charset="utf-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1" />
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<link
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rel="stylesheet"
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href="https://cdnjs.cloudflare.com/ajax/libs/github-markdown-css/5.7.0/github-markdown.min.css"
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/>
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<title>haunt98 posts</title>
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</head>
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<style>
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.markdown-body {
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box-sizing: border-box;
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min-width: 200px;
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max-width: 980px;
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margin: 0 auto;
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padding: 45px;
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font-family:
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Shantell Sans Normal,
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Rec Mono Casual,
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SF Pro,
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Inter,
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sans-serif;
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font-weight: 500;
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}
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.markdown-body pre {
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font-family:
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Berkeley Mono,
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IBM Plex Mono,
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SF Mono,
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Jetbrains Mono,
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monospace;
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}
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@media (max-width: 767px) {
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.markdown-body {
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padding: 15px;
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}
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}
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</style>
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<body class="markdown-body">
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<h2>
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<a href="index.html"><code>~</code></a>
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</h2>
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<div class="markdown-heading">
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<h1 class="heading-element">SQL</h1>
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<a
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id="user-content-sql"
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class="anchor"
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aria-label="Permalink: SQL"
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href="#sql"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Previously in my fresher software developer time, I rarely write SQL, I
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always use ORM to wrap SQL. But time past and too much abstraction bites
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me. So I decide to only write SQL from now as much as possible, no more
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ORM for me. But if there is any cool ORM for Go, I guess I try.
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</p>
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<p>
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This guide is not kind of guide which cover all cases. Just my little
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tricks when I work with SQL.
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</p>
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<div class="markdown-heading">
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<h2 class="heading-element">Stay away from database unique id</h2>
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<a
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id="user-content-stay-away-from-database-unique-id"
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class="anchor"
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aria-label="Permalink: Stay away from database unique id"
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href="#stay-away-from-database-unique-id"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Use UUID instead. If you can, and you should, choose UUID type which can
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be sortable.
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</p>
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<div class="markdown-heading">
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<h2 class="heading-element">Stay away from database timestamp</h2>
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<a
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id="user-content-stay-away-from-database-timestamp"
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class="anchor"
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aria-label="Permalink: Stay away from database timestamp"
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href="#stay-away-from-database-timestamp"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Stay away from all kind of database timestamp (MySQL timestamp, SQLite
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timestamp, ...) Just use int64 then pass the timestamp in service layer
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not database layer.
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</p>
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<p>
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Why? Because time and date and location are too much complex to handle. In
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my business, I use timestamp in milliseconds. Then I save timestamp as
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int64 value to database. Each time I get timestamp from database, I parse
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to time struct in Go with location or format I want. No more hassle!
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</p>
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<p>It looks like this:</p>
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<div class="highlight highlight-text-adblock">
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<pre>
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[Business] time, data -> convert to unix timestamp milliseconds -> [Database] int64</pre
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>
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</div>
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<div class="markdown-heading">
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<h2 class="heading-element">Extra field for extra things</h2>
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<a
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id="user-content-extra-field-for-extra-things"
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class="anchor"
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aria-label="Permalink: Extra field for extra things"
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href="#extra-field-for-extra-things"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Create new column in database is scary, so I suggest avoid it if you can.
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How to avoid, first design table with extra field. It is black hole, put
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everything in there if you want.
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</p>
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<p>I always use MySQL json data type for extra field.</p>
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<p>JSON data type is also useful for dumping request, response data.</p>
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<ul>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/5.7/en/json.html"
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rel="nofollow"
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>For MySQL 5.7</a
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>
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</li>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/8.0/en/json.html"
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rel="nofollow"
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>For MySQL 8.0</a
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>
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</li>
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</ul>
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<p>
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Use <code>JSON_EXTRACT(col, '$.key') IS NULL</code> to check json field
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exist or not.
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</p>
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<div class="markdown-heading">
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<h2 class="heading-element">Use index!!!</h2>
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<a
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id="user-content-use-index"
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class="anchor"
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aria-label="Permalink: Use index!!!"
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href="#use-index"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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You should use index for faster query, but not too much. Don't create
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index for every fields in table. Choose wisely!
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</p>
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<p>For example, create index in MySQL:</p>
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<div class="highlight highlight-source-sql">
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<pre><span class="pl-k">CREATE</span> <span class="pl-k">INDEX</span> <span class="pl-en">idx_user_id</span>
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<span class="pl-k">ON</span> user_upload (user_id);</pre>
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</div>
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<p>
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If create index inside <code>CREATE TABLE</code>,
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<a href="https://stackoverflow.com/a/1401615" rel="nofollow"
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>prefer <code>INDEX</code> to <code>KEY</code></a
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>:
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</p>
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<div class="highlight highlight-source-sql">
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<pre><span class="pl-k">CREATE</span> <span class="pl-k">TABLE</span> <span class="pl-en">user_upload</span>
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(
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id <span class="pl-k">int</span>(<span class="pl-c1">11</span>) <span class="pl-k">NOT NULL</span>,
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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>,
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<span class="pl-k">PRIMARY KEY</span> (id),
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INDEX idx_user_id (user_id)
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);</pre>
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</div>
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<p>Use <code>EXPLAIN</code> to check if index is used or not:</p>
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<ul>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/5.7/en/explain-output.html"
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rel="nofollow"
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>For MySQL 5.7</a
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>
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</li>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/8.0/en/explain-output.html"
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rel="nofollow"
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>For MySQL 8.0</a
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>
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</li>
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</ul>
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<div class="markdown-heading">
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<h2 class="heading-element">Be careful with UTF-8</h2>
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<a
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id="user-content-be-careful-with-utf-8"
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class="anchor"
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aria-label="Permalink: Be careful with UTF-8"
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href="#be-careful-with-utf-8"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>TLDR with MySQL:</p>
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<div class="highlight highlight-source-sql">
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<pre><span class="pl-k">CREATE</span> <span class="pl-k">TABLE</span> <span class="pl-en">ekyc_approved</span>
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(
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id <span class="pl-k">varchar</span>(<span class="pl-c1">30</span>) <span class="pl-k">NOT NULL</span>,
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<span class="pl-k">PRIMARY KEY</span> (id),
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) ENGINE <span class="pl-k">=</span> InnoDB
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DEFAULT CHARSET <span class="pl-k">=</span> utf8mb4;</pre>
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</div>
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<div class="markdown-heading">
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<h2 class="heading-element">Be careful with NULL</h2>
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<a
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id="user-content-be-careful-with-null"
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class="anchor"
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aria-label="Permalink: Be careful with NULL"
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href="#be-careful-with-null"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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If compare with field which can be NULL, remember to check NULL for
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safety.
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</p>
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<div class="highlight highlight-source-sql">
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<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>
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</div>
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<p>Need clarify why this happen? Idk :(</p>
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<div class="markdown-heading">
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<h2 class="heading-element"><code>VARCHAR</code> or <code>TEXT</code></h2>
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<a
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id="user-content-varchar-or-text"
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class="anchor"
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aria-label="Permalink: VARCHAR or TEXT"
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href="#varchar-or-text"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Prefer <code>VARCHAR</code> if you need to query and of course use index,
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and make sure size of value will never hit the limit. Prefer
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<code>TEXT</code> if you don't care, just want to store something.
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</p>
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<p>If you need to store UUID, use <code>VARCHAR(255)</code>.</p>
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<div class="markdown-heading">
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<h2 class="heading-element"><code>LIMIT</code></h2>
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<a
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id="user-content-limit"
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class="anchor"
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aria-label="Permalink: LIMIT"
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href="#limit"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Prefer <code>LIMIT 10 OFFSET 5</code> to <code>LIMIT 5, 10</code> to avoid
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misunderstanding.
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</p>
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<div class="markdown-heading">
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<h2 class="heading-element">
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Be super careful when migrate, update database on production and
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online!!!
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</h2>
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<a
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id="user-content-be-super-careful-when-migrate-update-database-on-production-and-online"
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class="anchor"
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aria-label="Permalink: Be super careful when migrate, update database on production and online!!!"
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href="#be-super-careful-when-migrate-update-database-on-production-and-online"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>
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Please read docs about online ddl operations before do anything online
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(keep database running the same time update it, for example create index,
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...)
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</p>
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<ul>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-operations.html"
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rel="nofollow"
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>For MySQL 5.7</a
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>,
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<a
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href="https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-limitations.html"
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rel="nofollow"
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>Limitations</a
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>
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</li>
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<li>
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<a
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href="https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-operations.html"
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rel="nofollow"
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>For MySQL 8.0</a
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>,
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<a
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href="https://dev.mysql.com/doc/refman/8.0/en/innodb-online-ddl-limitations.html"
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rel="nofollow"
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>Limitations</a
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>
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</li>
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</ul>
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<div class="markdown-heading">
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<h2 class="heading-element">Heathcheck</h2>
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<a
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id="user-content-heathcheck"
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class="anchor"
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aria-label="Permalink: Heathcheck"
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href="#heathcheck"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<p>Use <code>SELECT 1</code> to check if database failed yet.</p>
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<div class="markdown-heading">
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<h2 class="heading-element">Tools</h2>
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<a
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id="user-content-tools"
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class="anchor"
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aria-label="Permalink: Tools"
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href="#tools"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<ul>
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<li>
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Use
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<a href="https://github.com/sqlfluff/sqlfluff">sqlfluff/sqlfluff</a> to
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check your SQL.
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</li>
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<li>
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Use <a href="https://github.com/k1LoW/tbls">k1LoW/tbls</a> to grasp your
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database reality :)
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</li>
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</ul>
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<div class="markdown-heading">
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<h2 class="heading-element">Thanks</h2>
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<a
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id="user-content-thanks"
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class="anchor"
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aria-label="Permalink: Thanks"
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href="#thanks"
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><span aria-hidden="true" class="octicon octicon-link"></span
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></a>
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</div>
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<ul>
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<li>
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<p>
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<a href="https://use-the-index-luke.com/" rel="nofollow"
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>Use The Index, Luke</a
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>
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</p>
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</li>
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<li>
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<p>
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<a
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href="https://kevin.burke.dev/kevin/reddits-database-has-two-tables/"
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rel="nofollow"
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>Reddit’s database has two tables</a
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>
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</p>
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</li>
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<li>
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<p>
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<a
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href="https://shekhargulati.com/2022/07/08/my-notes-on-gitlabs-postgres-schema-design/"
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||
rel="nofollow"
|
||
>My Notes on GitLab Postgres Schema Design</a
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||
>
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||
</p>
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||
</li>
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||
<li>
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||
<p>
|
||
<a
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||
href="https://shekhargulati.com/2022/01/08/when-to-use-json-data-type-in-database-schema-design/"
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||
rel="nofollow"
|
||
>When to use JSON data type in database schema design?</a
|
||
>
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||
</p>
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||
</li>
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<li>
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||
<p>
|
||
<a
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||
href="https://planetscale.com/blog/how-read-mysql-explains"
|
||
rel="nofollow"
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||
>How to read MySQL EXPLAINs</a
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||
>
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||
</p>
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||
</li>
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<li>
|
||
<p>
|
||
<a
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||
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
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||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/a/43056611" rel="nofollow"
|
||
>Store UUID v4 in MySQL</a
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>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
||
<a href="https://stackoverflow.com/a/4849030" rel="nofollow"
|
||
>Difference between text and varchar (character varying)</a
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||
>
|
||
</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
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||
>
|
||
</p>
|
||
</li>
|
||
<li>
|
||
<p>
|
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<a href="https://stackoverflow.com/q/28888375" rel="nofollow"
|
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>Run a query with a LIMIT/OFFSET and also get the total number of
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rows</a
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>
|
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</p>
|
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</li>
|
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</ul>
|
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|
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<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>
|