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d484d2f684
This now gives a clean RAT check with bin/check-rat-report.py, which is one way for the Impala community to check compliance with ASF rules on intellectual property. Change-Id: I2ad06435f84a65ba126759e42a18fdaf52cd7036 Reviewed-on: http://gerrit.cloudera.org:8080/5232 Reviewed-by: Jim Apple <jbapple-impala@apache.org> Tested-by: Impala Public Jenkins Reviewed-by: John Russell <jrussell@cloudera.com>
169 lines
6.2 KiB
XML
169 lines
6.2 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="ddl">
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<title>DDL Statements</title>
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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="SQL"/>
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<data name="Category" value="DDL"/>
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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="Schemas"/>
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<data name="Category" value="Tables"/>
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<data name="Category" value="Databases"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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DDL refers to <q>Data Definition Language</q>, a subset of SQL statements that change the structure of the
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database schema in some way, typically by creating, deleting, or modifying schema objects such as databases,
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tables, and views. Most Impala DDL statements start with the keywords <codeph>CREATE</codeph>,
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<codeph>DROP</codeph>, or <codeph>ALTER</codeph>.
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</p>
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<p>
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The Impala DDL statements are:
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</p>
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<ul>
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<li>
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<xref href="impala_alter_table.xml#alter_table"/>
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</li>
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<li>
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<xref href="impala_alter_view.xml#alter_view"/>
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</li>
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<li>
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<xref href="impala_compute_stats.xml#compute_stats"/>
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</li>
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<li>
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<xref href="impala_create_database.xml#create_database"/>
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</li>
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<li>
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<xref href="impala_create_function.xml#create_function"/>
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</li>
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<li rev="2.0.0">
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<xref href="impala_create_role.xml#create_role"/>
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</li>
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<li>
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<xref href="impala_create_table.xml#create_table"/>
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</li>
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<li>
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<xref href="impala_create_view.xml#create_view"/>
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</li>
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<li>
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<xref href="impala_drop_database.xml#drop_database"/>
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</li>
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<li>
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<xref href="impala_drop_function.xml#drop_function"/>
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</li>
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<li rev="2.0.0">
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<xref href="impala_drop_role.xml#drop_role"/>
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</li>
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<li>
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<xref href="impala_drop_table.xml#drop_table"/>
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</li>
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<li>
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<xref href="impala_drop_view.xml#drop_view"/>
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</li>
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<li rev="2.0.0">
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<xref href="impala_grant.xml#grant"/>
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</li>
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<li rev="2.0.0">
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<xref href="impala_revoke.xml#revoke"/>
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</li>
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</ul>
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<p>
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After Impala executes a DDL command, information about available tables, columns, views, partitions, and so
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on is automatically synchronized between all the Impala nodes in a cluster. (Prior to Impala 1.2, you had to
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issue a <codeph>REFRESH</codeph> or <codeph>INVALIDATE METADATA</codeph> statement manually on the other
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nodes to make them aware of the changes.)
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</p>
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<p>
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If the timing of metadata updates is significant, for example if you use round-robin scheduling where each
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query could be issued through a different Impala node, you can enable the
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<xref href="impala_sync_ddl.xml#sync_ddl">SYNC_DDL</xref> query option to make the DDL statement wait until
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all nodes have been notified about the metadata changes.
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</p>
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<p rev="2.2.0">
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See <xref href="impala_s3.xml#s3"/> for details about how Impala DDL statements interact with
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tables and partitions stored in the Amazon S3 filesystem.
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</p>
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<p>
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Although the <codeph>INSERT</codeph> statement is officially classified as a DML (data manipulation language)
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statement, it also involves metadata changes that must be broadcast to all Impala nodes, and so is also
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affected by the <codeph>SYNC_DDL</codeph> query option.
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</p>
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<p>
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Because the <codeph>SYNC_DDL</codeph> query option makes each DDL operation take longer than normal, you
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might only enable it before the last DDL operation in a sequence. For example, if you are running a script
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that issues multiple of DDL operations to set up an entire new schema, add several new partitions, and so on,
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you might minimize the performance overhead by enabling the query option only before the last
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<codeph>CREATE</codeph>, <codeph>DROP</codeph>, <codeph>ALTER</codeph>, or <codeph>INSERT</codeph> statement.
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The script only finishes when all the relevant metadata changes are recognized by all the Impala nodes, so
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you could connect to any node and issue queries through it.
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</p>
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<p>
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The classification of DDL, DML, and other statements is not necessarily the same between Impala and Hive.
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Impala organizes these statements in a way intended to be familiar to people familiar with relational
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databases or data warehouse products. Statements that modify the metastore database, such as <codeph>COMPUTE
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STATS</codeph>, are classified as DDL. Statements that only query the metastore database, such as
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<codeph>SHOW</codeph> or <codeph>DESCRIBE</codeph>, are put into a separate category of utility statements.
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</p>
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<note>
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The query types shown in the Impala debug web user interface might not match exactly the categories listed
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here. For example, currently the <codeph>USE</codeph> statement is shown as DDL in the debug web UI. The
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query types shown in the debug web UI are subject to change, for improved consistency.
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</note>
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<p conref="../shared/impala_common.xml#common/related_info"/>
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<p>
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The other major classifications of SQL statements are data manipulation language (see
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<xref href="impala_dml.xml#dml"/>) and queries (see <xref href="impala_select.xml#select"/>).
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</p>
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</conbody>
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</concept>
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