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Change-Id: I07ec0a197de8a625788a3b0485d5ecf237e554ba Reviewed-on: http://gerrit.cloudera.org:8080/22576 Reviewed-by: Zoltan Borok-Nagy <boroknagyz@cloudera.com> Tested-by: Peter Rozsa <prozsa@cloudera.com>
99 lines
4.4 KiB
HTML
99 lines
4.4 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<meta name="copyright" content="(C) Copyright 2025" />
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<meta name="DC.rights.owner" content="(C) Copyright 2025" />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Overview of Impala Databases" />
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<meta name="DC.Relation" scheme="URI" content="../topics/impala_schema_objects.html" />
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<meta name="prodname" content="Impala" />
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<meta name="prodname" content="Impala" />
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<meta name="version" content="Impala 3.4.x" />
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<meta name="version" content="Impala 3.4.x" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="databases" />
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<link rel="stylesheet" type="text/css" href="../commonltr.css" />
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<title>Overview of Impala Databases</title>
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</head>
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<body id="databases">
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<h1 class="title topictitle1" id="ariaid-title1">Overview of Impala Databases</h1>
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<div class="body conbody">
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<p class="p">
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In Impala, a database is a logical container for a group of tables. Each database defines a separate
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namespace. Within a database, you can refer to the tables inside it using their unqualified names. Different
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databases can contain tables with identical names.
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</p>
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<p class="p"> Creating a database is a lightweight operation. There are minimal
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database-specific properties to configure, such as
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<code class="ph codeph">LOCATION</code> and <code class="ph codeph">COMMENT</code>. </p>
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<p class="p">You can change the owner of a database with the <code class="ph codeph">ALTER
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DATABASE</code> statement. </p>
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<p class="p">
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Typically, you create a separate database for each project or application, to avoid naming conflicts between
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tables and to make clear which tables are related to each other. The <code class="ph codeph">USE</code> statement lets
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you switch between databases. Unqualified references to tables, views, and functions refer to objects
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within the current database. You can also refer to objects in other databases by using qualified names
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of the form <code class="ph codeph"><var class="keyword varname">dbname</var>.<var class="keyword varname">object_name</var></code>.
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</p>
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<p class="p">
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Each database is physically represented by a directory in HDFS. When you do not specify a <code class="ph codeph">LOCATION</code>
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attribute, the directory is located in the Impala data directory with the associated tables managed by Impala.
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When you do specify a <code class="ph codeph">LOCATION</code> attribute, any read and write operations for tables in that
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database are relative to the specified HDFS directory.
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</p>
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<p class="p">
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There is a special database, named <code class="ph codeph">default</code>, where you begin when you connect to Impala.
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Tables created in <code class="ph codeph">default</code> are physically located one level higher in HDFS than all the
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user-created databases.
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</p>
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<div class="p">
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Impala includes another predefined database, <code class="ph codeph">_impala_builtins</code>, that
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serves as the location for the
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<a class="xref" href="../shared/../topics/impala_functions.html#builtins">built-in functions</a>. To see
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the built-in functions, use a statement like the following:
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<pre class="pre codeblock"><code>show functions in _impala_builtins;
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show functions in _impala_builtins like '*<var class="keyword varname">substring</var>*';
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</code></pre>
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</div>
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<p class="p">
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<strong class="ph b">Related statements:</strong>
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</p>
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<p class="p">
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<a class="xref" href="impala_create_database.html#create_database">CREATE DATABASE Statement</a>,
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<a class="xref" href="impala_drop_database.html#drop_database">DROP DATABASE Statement</a>, <a class="xref" href="impala_use.html#use">USE Statement</a>,
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<a class="xref" href="impala_show.html#show_databases">SHOW DATABASES</a>
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</p>
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</div>
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<div class="related-links">
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_schema_objects.html">Impala Schema Objects and Object Names</a></div>
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</div>
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</div></body>
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</html> |