impala/docs/topics/impala_misc_functions.xml

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<!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>

    <ul>
      <li>
        <xref href="#misc_functions/current_database">CURRENT_DATABASE</xref>
      </li>

      <li>
        <xref href="#misc_functions/effective_user">EFFECTIVE_USER</xref>
      </li>

      <li>
        <xref href="#misc_functions/get_json_object"
        >GET_JSON_OBJECT</xref>
      </li>

      <li>
        <xref href="#misc_functions/logged_in_user">LOGGED_IN_USER</xref>
      </li>

      <li>
        <xref href="#misc_functions/pid">PID</xref>
      </li>

      <li>
        <xref href="#misc_functions/sleep">SLEEP</xref>
      </li>

      <li>
        <xref href="#misc_functions/user">USER</xref>
      </li>

      <li>
        <xref href="#misc_functions/uuid">UUID</xref>
      </li>

      <li>
        <xref href="#misc_functions/version">VERSION</xref>
      </li>

      <li>
        <xref href="#misc_functions/coordinator">COORDINATOR</xref>
      </li>
    </ul>

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

        <dt>
          CURRENT_DATABASE()
        </dt>

        <dd>
          <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>
          EFFECTIVE_USER()
        </dt>

        <dd>
          <b>Purpose:</b> Typically returns the same value as <codeph>USER()</codeph>. If
          delegation is enabled, 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 id="get_json_object">

        <dt>
          GET_JSON_OBJECT(STRING json_str, STRING selector)
        </dt>

        <dd>
          <b>Purpose:</b> Extracts JSON object from the <varname>json_str</varname> based on the
          <varname>selector</varname> JSON path and returns the string of the extracted JSON
          object.
          <p>
            The function returns <codeph>NULL</codeph> if the input <varname>json_str</varname>
            is invalid or if nothing is selected based on the <varname>selector</varname> JSON
            path.
          </p>

          <p>
            The following characters are supported in the <varname>selector</varname> JSON path:
            <ul>
              <li>
                $ : Denotes the root object
              </li>

              <li>
                . : Denotes the child operator
              </li>

              <li>
                [] : Denotes the subscript operator for array
              </li>

              <li>
                * : Denotes the wildcard for [] or .
              </li>
            </ul>
          </p>

          <p>
            <b>Return type:</b> <codeph>STRING</codeph>
          </p>

          <p>
            <b>Examples:</b>
          </p>
<codeblock>---- QUERY
SELECT GET_JSON_OBJECT ('{"a":true, "b":false, "c":true}', '$.*');
---- RESULTS
[true,false,true]</codeblock>
<codeblock>---- QUERY
SELECT GET_JSON_OBJECT(t.json, '$.a.b.c') FROM (VALUES (
 ('{"a": {"b": {"c": 1}}}' AS json),
 ('{"a": {"b": {"c": 2}}}'),
 ('{"a": {"b": {"c": 3}}}')
)) t
---- RESULTS
'1'
'2'
'3'</codeblock>
<codeblock>---- QUERY
SELECT GET_JSON_OBJECT(t.json, '$.a'),
 GET_JSON_OBJECT(t.json, '$.b'),
 GET_JSON_OBJECT(t.json, '$.c')
FROM (VALUES (
 ('{"a":1, "b":2, "c":3}' AS json),
 ('{"b":2, "c":3}'),
 ('{"c":3}')
)) t
---- RESULTS
'1','2','3'
'NULL','2','3'
'NULL','NULL','3'</codeblock>
<codeblock>---- QUERY
SELECT GET_JSON_OBJECT(t.json, '$[1]'),
 GET_JSON_OBJECT(t.json, '$[*]')
FROM (VALUES (
 ('["a", "b", "c"]' AS json),
 ('["a", "b"]'),
 ('["a"]')
)) t
---- RESULTS
'b','["a","b","c"]'
'b','["a","b"]'
'NULL','a'</codeblock>
          <p>
            <b>Added in:</b> <keyword keyref="impala31"/>
          </p>
        </dd>

      </dlentry>

      <dlentry rev="3.1" id="logged_in_user">

        <dt>
          LOGGED_IN_USER()
        </dt>

        <dd>
          <b>Purpose:</b> Typically returns the same value as <codeph>USER()</codeph>. If
          delegation is enabled, it returns the ID of the delegated user.
          <p>
            <codeph>LOGGED_IN_USER()</codeph> is an alias of <codeph>EFFECTIVE_USER()</codeph>.
          </p>

          <p>
            <b>Return type:</b> <codeph>STRING</codeph>
          </p>

          <p>
            <b>Added in:</b> <keyword keyref="impala31"/>
          </p>
        </dd>

      </dlentry>

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

        <dt>
          PID()
        </dt>

        <dd>
          <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 id="sleep">

        <dt>
          SLEEP(INT ms)
        </dt>

        <dd>
          <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>
          USER()
        </dt>

        <dd>
          <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>
          UUID()
        </dt>

        <dd>
          <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>
            Each call to <codeph>UUID()</codeph> produces a new arbitrary value.
          </p>

          <p>
            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.
          </p>

          <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>
        </dd>

      </dlentry>

      <dlentry id="version">

        <dt>
          VERSION()
        </dt>

        <dd>
          <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>

      <dlentry id="coordinator" rev="IMPALA-589">

        <dt>
          COORDINATOR()
        </dt>

        <dd>
          <b>Purpose:</b> Returns the name of the host which is running the
          <codeph>impalad</codeph> daemon that is acting as the <codeph>coordinator</codeph> for
          the current query.
          <p>
            <b>Return type:</b> <codeph>STRING</codeph>
          </p>

          <p>
            <b>Added in:</b> <keyword keyref="impala31"/>
          </p>
        </dd>

      </dlentry>
    </dl>

  </conbody>

</concept>