318 lines
11 KiB
HTML
318 lines
11 KiB
HTML
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<div><a href="index.html">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-extra-field-for-extra-things"
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class="anchor"
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aria-hidden="true"
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href="#extra-field-for-extra-things"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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>Extra field for extra things
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</h2>
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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 also used for dumping request, response data.</p>
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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_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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<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 id="user-content-limit" class="anchor" aria-hidden="true" href="#limit"
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><span aria-hidden="true" class="octicon octicon-link"></span></a
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><code>LIMIT</code>
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</h2>
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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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<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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<li>
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<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"
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>When to use JSON data type in database schema design?</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://shekhargulati.com/2022/07/08/my-notes-on-gitlabs-postgres-schema-design/"
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rel="nofollow"
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>My Notes on GitLab Postgres Schema Design</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://planetscale.com/blog/how-read-mysql-explains"
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rel="nofollow"
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>How to read MySQL EXPLAINs</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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