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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>
92 lines
3.7 KiB
XML
92 lines
3.7 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="dml">
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<title>DML 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="DML"/>
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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="Tables"/>
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<data name="Category" value="ETL"/>
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<data name="Category" value="Ingest"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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DML refers to <q>Data Manipulation Language</q>, a subset of SQL statements that modify the data stored in
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tables. Because Impala focuses on query performance and leverages the append-only nature of HDFS storage,
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currently Impala only supports a small set of DML statements:
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</p>
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<ul>
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<li>
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<xref keyref="delete"/>. Works for Kudu tables only.
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</li>
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<li>
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<xref keyref="insert"/>.
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</li>
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<li>
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<xref keyref="load_data"/>. Does not apply for HBase or Kudu tables.
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</li>
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<li>
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<xref keyref="update"/>. Works for Kudu tables only.
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</li>
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<li>
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<xref keyref="upsert"/>. Works for Kudu tables only.
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</li>
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</ul>
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<p>
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<codeph>INSERT</codeph> in Impala is primarily optimized for inserting large volumes of data in a single
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statement, to make effective use of the multi-megabyte HDFS blocks. This is the way in Impala to create new
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data files. If you intend to insert one or a few rows at a time, such as using the <codeph>INSERT ...
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VALUES</codeph> syntax, that technique is much more efficient for Impala tables stored in HBase. See
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<xref href="impala_hbase.xml#impala_hbase"/> for details.
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</p>
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<p>
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<codeph>LOAD DATA</codeph> moves existing data files into the directory for an Impala table, making them
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immediately available for Impala queries. This is one way in Impala to work with data files produced by other
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Hadoop components. (<codeph>CREATE EXTERNAL TABLE</codeph> is the other alternative; with external tables,
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you can query existing data files, while the files remain in their original location.)
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</p>
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<p>
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In <keyword keyref="impala28_full"/> and higher, Impala does support the <codeph>UPDATE</codeph>, <codeph>DELETE</codeph>,
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and <codeph>UPSERT</codeph> statements for Kudu tables.
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For HDFS or S3 tables, to simulate the effects of an <codeph>UPDATE</codeph> or <codeph>DELETE</codeph> statement
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in other database systems, typically you use <codeph>INSERT</codeph> or <codeph>CREATE TABLE AS SELECT</codeph> to copy data
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from one table to another, filtering out or changing the appropriate rows during the copy operation.
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</p>
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<p>
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You can also achieve a result similar to <codeph>UPDATE</codeph> by using Impala tables stored in HBase.
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When you insert a row into an HBase table, and the table
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already contains a row with the same value for the key column, the older row is hidden, effectively the same
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as a single-row <codeph>UPDATE</codeph>.
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</p>
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<p rev="2.6.0">
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Impala can perform DML operations for tables or partitions stored in the Amazon S3 filesystem
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with <keyword keyref="impala26_full"/> and higher. See <xref href="impala_s3.xml#s3"/> for details.
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</p>
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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 definition language (see
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<xref href="impala_ddl.xml#ddl"/>) 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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