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Change-Id: I07ec0a197de8a625788a3b0485d5ecf237e554ba Reviewed-on: http://gerrit.cloudera.org:8080/22576 Reviewed-by: Zoltan Borok-Nagy <boroknagyz@cloudera.com> Tested-by: Peter Rozsa <prozsa@cloudera.com>
122 lines
5.2 KiB
HTML
122 lines
5.2 KiB
HTML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<meta name="copyright" content="(C) Copyright 2025" />
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<meta name="DC.rights.owner" content="(C) Copyright 2025" />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="DML Statements" />
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<meta name="DC.Relation" scheme="URI" content="../topics/impala_langref_sql.html" />
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<meta name="prodname" content="Impala" />
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<meta name="prodname" content="Impala" />
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<meta name="version" content="Impala 3.4.x" />
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<meta name="version" content="Impala 3.4.x" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="dml" />
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<link rel="stylesheet" type="text/css" href="../commonltr.css" />
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<title>DML Statements</title>
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</head>
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<body id="dml">
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<h1 class="title topictitle1" id="ariaid-title1">DML Statements</h1>
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<div class="body conbody">
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<p class="p">
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DML refers to <span class="q">"Data Manipulation Language"</span>, 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 class="ul">
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<li class="li">
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<a class="xref" href="impala_delete.html">DELETE Statement (Impala 2.8 or higher only)</a>. Works for Kudu tables only.
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</li>
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<li class="li">
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<a class="xref" href="impala_insert.html">INSERT Statement</a>.
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</li>
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<li class="li">
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<a class="xref" href="impala_load_data.html">LOAD DATA Statement</a>. Does not apply for HBase or Kudu tables.
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</li>
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<li class="li">
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<a class="xref" href="impala_update.html">UPDATE Statement (Impala 2.8 or higher only)</a>. Works for Kudu tables only.
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</li>
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<li class="li">
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<a class="xref" href="impala_upsert.html">UPSERT Statement (Impala 2.8 or higher only)</a>. Works for Kudu tables only.
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</li>
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</ul>
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<p class="p">
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<code class="ph codeph">INSERT</code> 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 <code class="ph codeph">INSERT ...
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VALUES</code> syntax, that technique is much more efficient for Impala tables stored in HBase. See
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<a class="xref" href="impala_hbase.html#impala_hbase">Using Impala to Query HBase Tables</a> for details.
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</p>
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<p class="p">
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<code class="ph codeph">LOAD DATA</code> 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. (<code class="ph codeph">CREATE EXTERNAL TABLE</code> 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 class="p">
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In <span class="keyword">Impala 2.8</span> and higher, Impala does support the <code class="ph codeph">UPDATE</code>, <code class="ph codeph">DELETE</code>,
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and <code class="ph codeph">UPSERT</code> statements for Kudu tables.
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For HDFS or S3 tables, to simulate the effects of an <code class="ph codeph">UPDATE</code> or <code class="ph codeph">DELETE</code> statement
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in other database systems, typically you use <code class="ph codeph">INSERT</code> or <code class="ph codeph">CREATE TABLE AS SELECT</code> 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 class="p">
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You can also achieve a result similar to <code class="ph codeph">UPDATE</code> 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 <code class="ph codeph">UPDATE</code>.
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</p>
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<p class="p">
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Impala can perform DML operations for tables or partitions stored in the Amazon S3 filesystem
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with <span class="keyword">Impala 2.6</span> and higher. See <a class="xref" href="impala_s3.html#s3">Using Impala with Amazon S3 Object Store</a> for details.
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</p>
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<p class="p">
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<strong class="ph b">Related information:</strong>
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</p>
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<p class="p">
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The other major classifications of SQL statements are data definition language (see
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<a class="xref" href="impala_ddl.html#ddl">DDL Statements</a>) and queries (see <a class="xref" href="impala_select.html#select">SELECT Statement</a>).
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</p>
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</div>
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<div class="related-links">
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_langref_sql.html">Impala SQL Statements</a></div>
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</div>
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</div></body>
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</html> |