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7.8 KiB
HTML
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<div class="section" id="faq">
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<h1>FAQ<a class="headerlink" href="#faq" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="can-i-query-join-multiple-tables-at-one-time">
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<h2>Can I query/join multiple tables at one time?<a class="headerlink" href="#can-i-query-join-multiple-tables-at-one-time" title="Permalink to this headline">¶</a></h2>
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<p>Not directly no. A Caravel SQLAlchemy datasource can only be a single table
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or a view.</p>
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<p>When working with tables, the solution would be to materialize
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a table that contains all the fields needed for your analysis, most likely
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through some scheduled batch process.</p>
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<p>A view is a simple logical layer that abstract an arbitrary SQL queries as
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a virtual table. This can allow you to join and union multiple tables, and
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to apply some transformation using arbitrary SQL expressions. The limitation
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there is your database performance as Caravel effectively will run a query
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on top of your query (view). A good practice may be to limit yourself to
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joining your main large table to one or many small tables only, and avoid
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using <code class="docutils literal"><span class="pre">GROUP</span> <span class="pre">BY</span></code> where possible as Caravel will do its own <code class="docutils literal"><span class="pre">GROUP</span> <span class="pre">BY</span></code> and
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doing the work twice might slow down performance.</p>
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<p>Whether you use a table or a view, the important factor is whether your
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database is fast enough to serve it in an interactive fashion to provide
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a good user experience in Caravel.</p>
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</div>
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<div class="section" id="how-big-can-my-data-source-be">
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<h2>How BIG can my data source be?<a class="headerlink" href="#how-big-can-my-data-source-be" title="Permalink to this headline">¶</a></h2>
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<p>It can be gigantic! As mentioned above, the main criteria is whether your
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database can execute queries and return results in a time frame that is
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acceptable to your users. Many distributed databases out there can execute
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queries that scan through terabytes in an interactive fashion.</p>
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</div>
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<div class="section" id="how-do-i-create-my-own-visualization">
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<h2>How do I create my own visualization?<a class="headerlink" href="#how-do-i-create-my-own-visualization" title="Permalink to this headline">¶</a></h2>
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<p>We are planning on making it easier to add new visualizations to the
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framework, in the meantime, we’ve tagged a few pull requests as
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<code class="docutils literal"><span class="pre">example</span></code> to give people examples of how to contribute new
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visualizations.</p>
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<p><a class="reference external" href="https://github.com/airbnb/caravel/issues?q=label%3Aexample+is%3Aclosed">https://github.com/airbnb/caravel/issues?q=label%3Aexample+is%3Aclosed</a></p>
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