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Change-Id: Ifac0b689d55f525145b37846967a7a22f0e9245b Reviewed-on: http://gerrit.cloudera.org:8080/11674 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Adam Holley <aholley@cloudera.com> Reviewed-by: Fredy Wijaya <fwijaya@cloudera.com>
85 lines
3.6 KiB
XML
85 lines
3.6 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="databases">
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<title>Overview of Impala Databases</title>
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<titlealts audience="PDF"><navtitle>Databases</navtitle></titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Databases"/>
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<data name="Category" value="SQL"/>
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<data name="Category" value="Data Analysts"/>
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<data name="Category" value="Developers"/>
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<data name="Category" value="Querying"/>
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<data name="Category" value="Schemas"/>
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</metadata>
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</prolog>
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<conbody>
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<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> 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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<codeph>LOCATION</codeph> and <codeph>COMMENT</codeph>. </p>
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<p>You can change the owner of a database with the <codeph>ALTER
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DATABASE</codeph> statement. </p>
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<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 <codeph>USE</codeph> 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 <codeph><varname>dbname</varname>.<varname>object_name</varname></codeph>.
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</p>
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<p>
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Each database is physically represented by a directory in HDFS. When you do not specify a <codeph>LOCATION</codeph>
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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 <codeph>LOCATION</codeph> 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>
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There is a special database, named <codeph>default</codeph>, where you begin when you connect to Impala.
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Tables created in <codeph>default</codeph> 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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<p conref="../shared/impala_common.xml#common/builtins_db"/>
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<p>
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<b>Related statements:</b>
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</p>
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<p>
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<xref href="impala_create_database.xml#create_database"/>,
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<xref href="impala_drop_database.xml#drop_database"/>, <xref href="impala_use.xml#use"/>,
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<xref href="impala_show.xml#show_databases"/>
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</p>
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</conbody>
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</concept>
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