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e8ee827a6d
- The function titles were changed to upper case. - The function titles no longer use <codeph>. <codeph> font appears smaller than the <p> font. - Return type were changed to upper case data types. - Minor typos were fixed, such as extra commas and periods in titles. - The indexterm dita elememts were removed. Indexterm was incomplete and WIP. No plan to go ahead and implement it, so removed. Change-Id: I797532463da8d29fe5bc7543cfdfb5b2b82db197 Reviewed-on: http://gerrit.cloudera.org:8080/11619 Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com> Reviewed-by: Michael Brown <mikeb@cloudera.com>
291 lines
9.0 KiB
XML
291 lines
9.0 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="misc_functions">
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<title>Impala Miscellaneous Functions</title>
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<titlealts audience="PDF">
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<navtitle>Miscellaneous Functions</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 Functions"/>
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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="Querying"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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Impala supports the following utility functions that do not operate on a particular column
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or data type:
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</p>
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<ul>
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<li>
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<xref href="#misc_functions/current_database">CURRENT_DATABASE</xref>
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</li>
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<li>
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<xref href="#misc_functions/effective_user">EFFECTIVE_USER</xref>
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</li>
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<li>
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<xref href="#misc_functions/pid">PID</xref>
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</li>
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<li>
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<xref href="#misc_functions/sleep">SLEEP</xref>
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</li>
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<li>
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<xref href="#misc_functions/user">USER</xref>
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</li>
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<li>
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<xref href="#misc_functions/uuid">UUID</xref>
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</li>
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<li>
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<xref href="#misc_functions/version">VERSION</xref>
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</li>
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<li>
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<xref href="#misc_functions/coordinator">COORDINATOR</xref>
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</li>
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</ul>
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<dl>
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<dlentry rev="1.3.0" id="current_database">
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<dt>
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CURRENT_DATABASE()
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</dt>
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<dd>
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<b>Purpose:</b> Returns the database that the session is currently using, either
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<codeph>default</codeph> if no database has been selected, or whatever database the
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session switched to through a <codeph>USE</codeph> statement or the
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<cmdname>impalad</cmdname> <codeph>-d</codeph> option.
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<p>
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<b>Return type:</b> <codeph>STRING</codeph>
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</p>
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</dd>
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</dlentry>
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<dlentry rev="5.4.5" id="effective_user">
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<dt>
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EFFECTIVE_USER()
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</dt>
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<dd>
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<b>Purpose:</b> Typically returns the same value as <codeph>USER()</codeph>. If
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delegation is enabled, it returns the ID of the delegated user.
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<p>
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<b>Return type:</b> <codeph>STRING</codeph>
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</p>
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<p>
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<b>Added in:</b> <keyword keyref="impala225"/>
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</p>
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</dd>
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</dlentry>
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<dlentry rev="1.3.0" id="pid">
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<dt>
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PID()
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</dt>
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<dd>
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<b>Purpose:</b> Returns the process ID of the <cmdname>impalad</cmdname> daemon that
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the session is connected to. You can use it during low-level debugging, to issue Linux
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commands that trace, show the arguments, and so on the <cmdname>impalad</cmdname>
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process.
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<p>
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<b>Return type:</b> <codeph>INT</codeph>
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</p>
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</dd>
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</dlentry>
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<dlentry id="sleep">
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<dt>
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SLEEP(INT ms)
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</dt>
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<dd>
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<b>Purpose:</b> Pauses the query for a specified number of milliseconds. For slowing
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down queries with small result sets enough to monitor runtime execution, memory usage,
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or other factors that otherwise would be difficult to capture during the brief
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interval of query execution. When used in the <codeph>SELECT</codeph> list, it is
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called once for each row in the result set; adjust the number of milliseconds
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accordingly. For example, a query <codeph>SELECT *, SLEEP(5) FROM
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table_with_1000_rows</codeph> would take at least 5 seconds to complete (5
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milliseconds * 1000 rows in result set). To avoid an excessive number of concurrent
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queries, use this function for troubleshooting on test and development systems, not
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for production queries.
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<p>
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<b>Return type:</b> N/A
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</p>
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</dd>
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</dlentry>
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<dlentry rev="1.1" id="user">
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<dt>
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USER()
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</dt>
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<dd>
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<b>Purpose:</b> Returns the username of the Linux user who is connected to the
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<cmdname>impalad</cmdname> daemon. Typically called a single time, in a query without
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any <codeph>FROM</codeph> clause, to understand how authorization settings apply in a
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security context; once you know the logged-in username, you can check which groups
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that user belongs to, and from the list of groups you can check which roles are
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available to those groups through the authorization policy file.
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<p conref="../shared/impala_common.xml#common/user_kerberized"/>
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<p>
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When delegation is enabled, consider calling the <codeph>EFFECTIVE_USER()</codeph>
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function instead.
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</p>
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<p>
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<b>Return type:</b> <codeph>STRING</codeph>
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</p>
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</dd>
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</dlentry>
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<dlentry rev="2.5.0 IMPALA-1477" id="uuid">
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<dt>
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UUID()
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</dt>
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<dd>
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<b>Purpose:</b> Returns a
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<xref
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href="https://en.wikipedia.org/wiki/Universally_unique_identifier"
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scope="external" format="html">universal
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unique identifier</xref>, a 128-bit value encoded as a string with groups of
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hexadecimal digits separated by dashes.
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<p>
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<b>Return type:</b> <codeph>STRING</codeph>
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</p>
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<p conref="../shared/impala_common.xml#common/added_in_250"/>
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<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
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<p>
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Ascending numeric sequences of type <codeph>BIGINT</codeph> are often used as
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identifiers within a table, and as join keys across multiple tables. The
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<codeph>UUID()</codeph> value is a convenient alternative that does not require
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storing or querying the highest sequence number. For example, you can use it to
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quickly construct new unique identifiers during a data import job, or to combine
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data from different tables without the likelihood of ID collisions.
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</p>
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<p conref="../shared/impala_common.xml#common/example_blurb"/>
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<codeblock>
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-- Each call to uuid() produces a new arbitrary value.
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select uuid();
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+--------------------------------------+
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| uuid() |
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+--------------------------------------+
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| c7013e25-1455-457f-bf74-a2046e58caea |
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+--------------------------------------+
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-- If you get a UUID for each row of a result set, you can use it as a
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-- unique identifier within a table, or even a unique ID across tables.
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select uuid() from four_row_table;
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+--------------------------------------+
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| uuid() |
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+--------------------------------------+
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| 51d3c540-85e5-4cb9-9110-604e53999e2e |
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| 0bb40071-92f6-4a59-a6a4-60d46e9703e2 |
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| 5e9d7c36-9842-4a96-862d-c13cd0457c02 |
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| cae29095-0cc0-4053-a5ea-7fcd3c780861 |
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+--------------------------------------+
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</codeblock>
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</dd>
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</dlentry>
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<dlentry id="version">
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<dt>
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VERSION()
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</dt>
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<dd>
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<b>Purpose:</b> Returns information such as the precise version number and build date
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for the <codeph>impalad</codeph> daemon that you are currently connected to. Typically
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used to confirm that you are connected to the expected level of Impala to use a
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particular feature, or to connect to several nodes and confirm they are all running
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the same level of <cmdname>impalad</cmdname>.
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<p>
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<b>Return type:</b> <codeph>STRING</codeph> (with one or more embedded newlines)
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</p>
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</dd>
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</dlentry>
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<dlentry id="coordinator" rev="IMPALA-589">
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<dt>
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COORDINATOR()
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</dt>
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<dd>
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<b>Purpose:</b> Returns the name of the host which is running the
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<codeph>impalad</codeph> daemon that is acting as the <codeph>coordinator</codeph> for
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the current query.
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<p>
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<b>Return type:</b> <codeph>STRING</codeph>
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</p>
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<p>
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<b>Added in:</b> <keyword keyref="impala31"/>
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</p>
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</dd>
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</dlentry>
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</dl>
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</conbody>
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</concept>
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