mirror of
https://github.com/apache/impala.git
synced 2026-01-08 21:03:01 -05:00
3be0f122a5
These are refugees from doc_prototype. They can be rendered with the DITA Open Toolkit version 2.3.3 by: /tmp/dita-ot-2.3.3/bin/dita \ -i impala.ditamap \ -f html5 \ -o $(mktemp -d) \ -filter impala_html.ditaval Change-Id: I8861e99adc446f659a04463ca78c79200669484f Reviewed-on: http://gerrit.cloudera.org:8080/5014 Reviewed-by: John Russell <jrussell@cloudera.com> Tested-by: John Russell <jrussell@cloudera.com>
66 lines
2.8 KiB
XML
66 lines
2.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!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,
|
|
only <codeph>LOCATION</codeph> and <codeph>COMMENT</codeph>. There is no <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>
|