257 lines
8.6 KiB
HTML
257 lines
8.6 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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.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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@media (max-width: 767px) {
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padding: 15px;
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font-family: "Martian Mono", monospace;
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</style>
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<body class="markdown-body">
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<div><a href="index">Index</a></div>
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<h1>
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<a id="user-content-sql" class="anchor" aria-hidden="true" href="#sql"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>SQL
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</h1>
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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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<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-hidden="true"
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href="#stay-away-from-database-unique-id"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Stay away from database unique id
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</h2>
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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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<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-hidden="true"
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href="#stay-away-from-database-timestamp"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Stay away from database timestamp
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</h2>
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<p>
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Stay away from all kind of database timestamp (MySQL timestmap, 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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<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-hidden="true"
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href="#use-index"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Use index!!!
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</h2>
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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_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>
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</div>
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<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-hidden="true"
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href="#be-careful-with-null"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Be careful with NULL
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</h2>
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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 happpen? Idk :(</p>
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<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-hidden="true"
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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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<code>VARCHAR</code> or <code>TEXT</code>
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</h2>
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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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<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-hidden="true"
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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></a
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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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<p>
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Plase 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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<h2>
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<a id="user-content-tools" class="anchor" aria-hidden="true" href="#tools"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Tools
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</h2>
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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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<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-hidden="true"
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href="#thanks"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Thanks
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</h2>
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<ul>
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<li>
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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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</li>
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<li>
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<a
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href="https://www.foxhound.systems/blog/essential-elements-of-high-performance-sql-indexes/"
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rel="nofollow"
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>Essential elements of high performance applications: SQL indexes</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://architecturenotes.co/things-you-should-know-about-databases/"
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rel="nofollow"
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>Things You Should Know About Databases</a
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>
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</li>
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</ul>
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<div>
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Feel free to ask me via
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<a href="mailto:hauvipapro+posts@gmail.com">email</a> or
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<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>. Source
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code is available on
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<a href="https://github.com/haunt98/posts-go">GitHub</a>
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</div>
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</body>
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</html>
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