docs/topics/impala_databases.xml

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="databases">

  <title>Overview of Impala Databases</title>
  <titlealts audience="PDF"><navtitle>Databases</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Databases"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Data Analysts"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Querying"/>
      <data name="Category" value="Schemas"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      In Impala, a database is a logical container for a group of tables. Each database defines a separate
      namespace. Within a database, you can refer to the tables inside it using their unqualified names. Different
      databases can contain tables with identical names.
    </p>

    <p> Creating a database is a lightweight operation. There are minimal
      database-specific properties to configure, such as
        <codeph>LOCATION</codeph> and <codeph>COMMENT</codeph>. </p>
    <p>You can change the owner of a database with the <codeph>ALTER
        DATABASE</codeph> statement. </p>

    <p>
      Typically, you create a separate database for each project or application, to avoid naming conflicts between
      tables and to make clear which tables are related to each other. The <codeph>USE</codeph> statement lets
      you switch between databases. Unqualified references to tables, views, and functions refer to objects
      within the current database. You can also refer to objects in other databases by using qualified names
      of the form <codeph><varname>dbname</varname>.<varname>object_name</varname></codeph>.
    </p>

    <p>
      Each database is physically represented by a directory in HDFS. When you do not specify a <codeph>LOCATION</codeph>
      attribute, the directory is located in the Impala data directory with the associated tables managed by Impala.
      When you do specify a <codeph>LOCATION</codeph> attribute, any read and write operations for tables in that
      database are relative to the specified HDFS directory.
    </p>

    <p>
      There is a special database, named <codeph>default</codeph>, where you begin when you connect to Impala.
      Tables created in <codeph>default</codeph> are physically located one level higher in HDFS than all the
      user-created databases.
    </p>

    <p conref="../shared/impala_common.xml#common/builtins_db"/>

    <p>
      <b>Related statements:</b>
    </p>

    <p>
      <xref href="impala_create_database.xml#create_database"/>,
      <xref href="impala_drop_database.xml#drop_database"/>, <xref href="impala_use.xml#use"/>,
      <xref href="impala_show.xml#show_databases"/>
    </p>
  </conbody>
</concept>