docs/topics/impala_create_database.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="create_database">

  <title>CREATE DATABASE Statement</title>
  <titlealts audience="PDF"><navtitle>CREATE DATABASE</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Databases"/>
      <data name="Category" value="Schemas"/>
      <data name="Category" value="DDL"/>
      <data name="Category" value="S3"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      <indexterm audience="hidden">CREATE DATABASE statement</indexterm>
      Creates a new database.
    </p>

    <p>
      In Impala, a database is both:
    </p>

    <ul>
      <li>
        A logical construct for grouping together related tables, views, and functions within their own namespace.
        You might use a separate database for each application, set of related tables, or round of experimentation.
      </li>

      <li>
        A physical construct represented by a directory tree in HDFS. Tables (internal tables), partitions, and
        data files are all located under this directory. You can perform HDFS-level operations such as backing it up and measuring space usage,
        or remove it with a <codeph>DROP DATABASE</codeph> statement.
      </li>
    </ul>

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

<codeblock>CREATE (DATABASE|SCHEMA) [IF NOT EXISTS] <varname>database_name</varname>[COMMENT '<varname>database_comment</varname>']
  [LOCATION <varname>hdfs_path</varname>];</codeblock>

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

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

    <p>
      A database is physically represented as a directory in HDFS, with a filename extension <codeph>.db</codeph>,
      under the main Impala data directory. If the associated HDFS directory does not exist, it is created for you.
      All databases and their associated directories are top-level objects, with no physical or logical nesting.
    </p>

    <p>
      After creating a database, to make it the current database within an <cmdname>impala-shell</cmdname> session,
      use the <codeph>USE</codeph> statement. You can refer to tables in the current database without prepending
      any qualifier to their names.
    </p>

    <p>
      When you first connect to Impala through <cmdname>impala-shell</cmdname>, the database you start in (before
      issuing any <codeph>CREATE DATABASE</codeph> or <codeph>USE</codeph> statements) is named
      <codeph>default</codeph>.
    </p>

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

    <p>
      After creating a database, your <cmdname>impala-shell</cmdname> session or another
      <cmdname>impala-shell</cmdname> connected to the same node can immediately access that database. To access
      the database through the Impala daemon on a different node, issue the <codeph>INVALIDATE METADATA</codeph>
      statement first while connected to that other node.
    </p>

    <p>
      Setting the <codeph>LOCATION</codeph> attribute for a new database is a way to work with sets of files in an
      HDFS directory structure outside the default Impala data directory, as opposed to setting the
      <codeph>LOCATION</codeph> attribute for each individual table.
    </p>

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

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

    <p>
      When you create a database in Impala, the database can also be used by Hive.
      When you create a database in Hive, issue an <codeph>INVALIDATE METADATA</codeph>
      statement in Impala to make Impala permanently aware of the new database.
    </p>

    <p>
      The <codeph>SHOW DATABASES</codeph> statement lists all databases, or the databases whose name
      matches a wildcard pattern. <ph rev="2.5.0">In <keyword keyref="impala25_full"/> and higher, the
      <codeph>SHOW DATABASES</codeph> output includes a second column that displays the associated
      comment, if any, for each database.</ph>
    </p>

    <p conref="../shared/impala_common.xml#common/s3_blurb"/>

    <p rev="2.6.0 IMPALA-1878">
      To specify that any tables created within a database reside on the Amazon S3 system,
      you can include an <codeph>s3a://</codeph> prefix on the <codeph>LOCATION</codeph>
      attribute. In <keyword keyref="impala26_full"/> and higher, Impala automatically creates any
      required folders as the databases, tables, and partitions are created, and removes
      them when they are dropped.
    </p>

    <p conref="../shared/impala_common.xml#common/s3_ddl"/>

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

    <p conref="../shared/impala_common.xml#common/permissions_blurb"/>
    <p rev="">
      The user ID that the <cmdname>impalad</cmdname> daemon runs under,
      typically the <codeph>impala</codeph> user, must have write
      permission for the parent HDFS directory under which the database
      is located.
    </p>

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

    <codeblock conref="../shared/impala_common.xml#common/create_drop_db_example"/>

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

    <p>
      <xref href="impala_databases.xml#databases"/>, <xref href="impala_drop_database.xml#drop_database"/>,
      <xref href="impala_use.xml#use"/>, <xref href="impala_show.xml#show_databases"/>,
      <xref href="impala_tables.xml#tables"/>
    </p>
  </conbody>
</concept>