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Currently, the two topics, Querying Arrays and Zipping Unnest on Arrays from Views, were missing. The documentation has been added, and the parent topic has been updated with references to the child topics. Change-Id: I3ad29153bf6ed3939fb1d87d6220bd22f8f7fa1b Reviewed-on: http://gerrit.cloudera.org:8080/21651 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Quanlong Huang <huangquanlong@gmail.com>
81 lines
3.6 KiB
XML
81 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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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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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="impala_unnest_views" rev="4.1.0">
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<title>Zipping unnest on arrays from views (<keyword keyref="impala41"/> or higher only)</title>
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<titlealts audience="PDF">
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<navtitle>Zipping unnest on arrays from views</navtitle>
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</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="Impala Data Types"/>
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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="Schemas"/>
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</metadata>
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</prolog>
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<conbody>
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<p rev="4.1.0">
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<indexterm audience="hidden">Zipping unnest on arrays from views</indexterm>
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<keyword keyref="impala41"/>, the zipping unnest functionality works for arrays in both tables
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and
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views.<codeblock id="codeblock_nwz_lyc_3cc">SELECT UNNSET(arr1) FROM view_name;</codeblock>
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</p>
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<section id="section_irf_rrb_3cc">
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<title>UNNEST() on array columns</title>
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<p>You can use <codeph>UNNEST()</codeph> on array columns in two ways. Using one of these two
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ways results in the items of the arrays being zipped together instead of joining.</p>
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<ul id="ul_jrf_rrb_3cc">
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<li>ISO:SQL 2016 compliant syntax</li>
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</ul>
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<codeblock id="codeblock_krf_rrb_3cc">SELECT a1.item, a2.item
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FROM complextypes_arrays t, UNNEST(t.arr1, t.arr2) AS (a1, a2);
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</codeblock>
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<ul id="ul_lrf_rrb_3cc">
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<li>Postgres compatible syntax</li>
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</ul>
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<codeblock id="codeblock_mrf_rrb_3cc">SELECT UNNEST(arr1), UNNEST(arr2) FROM complextypes_arrays;</codeblock>
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<p>When unnesting multiple arrays with zipping unnest, the i'th item of one array will be
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placed next to the i'th item of the other arrays in the results. If the size of the arrays
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is not equal then the shorter arrays will be filled with NULL values up to the size of the
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longest array as shown in the following example:</p>
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<p>The test data used in this example is arr1: {1, 2, 3}, arr2: {11, 12}</p>
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<p>After running any of the queries listed in the examples, the result will be as shown
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here:</p>
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<p>
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<codeblock id="codeblock_n5z_cjq_mtb">arr1 arr2
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[1, 11]
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[2, 12]
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[3, NULL]
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</codeblock>
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</p>
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</section>
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<section id="section_ifc_trb_3cc">
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<title>Example of an UNNEST() in an inline view using SELECT/FILTER of the inline view</title>
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<p>In the following example the filter is not in the <codeph>SELECT</codeph> query that
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creates the inline view but a level above that.</p>
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<codeblock id="codeblock_jfc_trb_3cc">SELECT id, ac1, ac2 FROM (SELECT id, UNNEST(array_col1) AS ac1, UNNEST(array_col2) AS ac2 FROM some_view) WHERE id <10;
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</codeblock>
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</section>
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</conbody>
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</concept>
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