impala/docs/topics/impala_misc_functions.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="misc_functions">

  <title>Impala Miscellaneous Functions</title>
  <titlealts audience="PDF"><navtitle>Miscellaneous Functions</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Functions"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Data Analysts"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Querying"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      Impala supports the following utility functions that do not operate on a particular column or data type:
    </p>

    <dl>
      <dlentry rev="1.3.0" id="current_database">

        <dt>
          <codeph>current_database()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">current_database() function</indexterm>
          <b>Purpose:</b> Returns the database that the session is currently using, either <codeph>default</codeph>
          if no database has been selected, or whatever database the session switched to through a
          <codeph>USE</codeph> statement or the <cmdname>impalad</cmdname><codeph>-d</codeph> option.
          <p>
            <b>Return type:</b> <codeph>string</codeph>
          </p>
        </dd>

      </dlentry>

      <dlentry rev="5.4.5" id="effective_user">

        <dt>
          <codeph>effective_user()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">effective_user() function</indexterm>
          <b>Purpose:</b> Typically returns the same value as <codeph>user()</codeph>,
          except if delegation is enabled, in which case it returns the ID of the delegated user.
          <p>
            <b>Return type:</b> <codeph>string</codeph>
          </p>
          <p>
            <b>Added in:</b> <keyword keyref="impala225"/>
          </p>
        </dd>

      </dlentry>

      <dlentry rev="1.3.0" id="pid">

        <dt>
          <codeph>pid()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">pid() function</indexterm>
          <b>Purpose:</b> Returns the process ID of the <cmdname>impalad</cmdname> daemon that the session is
          connected to. You can use it during low-level debugging, to issue Linux commands that trace, show the
          arguments, and so on the <cmdname>impalad</cmdname> process.
          <p>
            <b>Return type:</b> <codeph>int</codeph>
          </p>
        </dd>

      </dlentry>

      <dlentry audience="hidden" id="sleep">

        <dt>
          <codeph>sleep(int ms)</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">sleep() function</indexterm>
          <b>Purpose:</b> Pauses the query for a specified number of milliseconds. For slowing down queries with
          small result sets enough to monitor runtime execution, memory usage, or other factors that otherwise
          would be difficult to capture during the brief interval of query execution. When used in the
          <codeph>SELECT</codeph> list, it is called once for each row in the result set; adjust the number of
          milliseconds accordingly. For example, a query <codeph>SELECT *, sleep(5) FROM
          table_with_1000_rows</codeph> would take at least 5 seconds to complete (5 milliseconds * 1000 rows in
          result set). To avoid an excessive number of concurrent queries, use this function for troubleshooting on
          test and development systems, not for production queries.
          <p>
            <b>Return type:</b> N/A
          </p>
        </dd>

      </dlentry>

      <dlentry rev="1.1" id="user">

        <dt>
          <codeph>user()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">user() function</indexterm>
          <b>Purpose:</b> Returns the username of the Linux user who is connected to the <cmdname>impalad</cmdname>
          daemon. Typically called a single time, in a query without any <codeph>FROM</codeph> clause, to
          understand how authorization settings apply in a security context; once you know the logged-in username,
          you can check which groups that user belongs to, and from the list of groups you can check which roles
          are available to those groups through the authorization policy file.
          <p conref="../shared/impala_common.xml#common/user_kerberized"/>
          <p>
            When delegation is enabled, consider calling the <codeph>effective_user()</codeph> function instead.
          </p>
          <p>
            <b>Return type:</b> <codeph>string</codeph>
          </p>
        </dd>

      </dlentry>

      <dlentry rev="2.5.0 IMPALA-1477" id="uuid">

        <dt>
          <codeph>uuid()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">uuid() function</indexterm>
          <b>Purpose:</b> Returns a <xref href="https://en.wikipedia.org/wiki/Universally_unique_identifier" scope="external" format="html">universal unique identifier</xref>, a 128-bit value encoded as a string with groups of hexadecimal digits separated by dashes.
          <p>
            <b>Return type:</b> <codeph>string</codeph>
          </p>
          <p conref="../shared/impala_common.xml#common/added_in_250"/>
          <p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
          <p>
            Ascending numeric sequences of type <codeph>BIGINT</codeph> are often used
            as identifiers within a table, and as join keys across multiple tables.
            The <codeph>uuid()</codeph> value is a convenient alternative that does not
            require storing or querying the highest sequence number. For example, you
            can use it to quickly construct new unique identifiers during a data import job,
            or to combine data from different tables without the likelihood of ID collisions.
          </p>
          <p conref="../shared/impala_common.xml#common/example_blurb"/>
<codeblock>
-- Each call to uuid() produces a new arbitrary value.
select uuid();
+--------------------------------------+
| uuid()                               |
+--------------------------------------+
| c7013e25-1455-457f-bf74-a2046e58caea |
+--------------------------------------+

-- If you get a UUID for each row of a result set, you can use it as a
-- unique identifier within a table, or even a unique ID across tables.
select uuid() from four_row_table;
+--------------------------------------+
| uuid()                               |
+--------------------------------------+
| 51d3c540-85e5-4cb9-9110-604e53999e2e |
| 0bb40071-92f6-4a59-a6a4-60d46e9703e2 |
| 5e9d7c36-9842-4a96-862d-c13cd0457c02 |
| cae29095-0cc0-4053-a5ea-7fcd3c780861 |
+--------------------------------------+
</codeblock>
        </dd>

      </dlentry>

      <dlentry id="version">

        <dt>
          <codeph>version()</codeph>
        </dt>

        <dd>
          <indexterm audience="hidden">version() function</indexterm>
          <b>Purpose:</b> Returns information such as the precise version number and build date for the
          <codeph>impalad</codeph> daemon that you are currently connected to. Typically used to confirm that you
          are connected to the expected level of Impala to use a particular feature, or to connect to several nodes
          and confirm they are all running the same level of <cmdname>impalad</cmdname>.
          <p>
            <b>Return type:</b> <codeph>string</codeph> (with one or more embedded newlines)
          </p>
        </dd>

      </dlentry>
    </dl>
  </conbody>
</concept>