docs/topics/impala_offset.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept rev="1.2.1" id="offset">

  <title>OFFSET Clause</title>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Querying"/>
      <data name="Category" value="Reports"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      The <codeph>OFFSET</codeph> clause in a <codeph>SELECT</codeph> query causes the result set to start some
      number of rows after the logical first item. The result set is numbered starting from zero, so <codeph>OFFSET
      0</codeph> produces the same result as leaving out the <codeph>OFFSET</codeph> clause. Always use this clause
      in combination with <codeph>ORDER BY</codeph> (so that it is clear which item should be first, second, and so
      on) and <codeph>LIMIT</codeph> (so that the result set covers a bounded range, such as items 0-9, 100-199,
      and so on).
    </p>

    <p conref="../shared/impala_common.xml#common/limit_and_offset"/>

    <p conref="../shared/impala_common.xml#common/example_blurb"/>

    <p>
      The following example shows how you could run a <q>paging</q> query originally written for a traditional
      database application. Because typical Impala queries process megabytes or gigabytes of data and read large
      data files from disk each time, it is inefficient to run a separate query to retrieve each small group of
      items. Use this technique only for compatibility while porting older applications, then rewrite the
      application code to use a single query with a large result set, and display pages of results from the cached
      result set.
    </p>

<codeblock>[localhost:21000] &gt; create table numbers (x int);
[localhost:21000] &gt; insert into numbers select x from very_long_sequence;
Inserted 1000000 rows in 1.34s
[localhost:21000] &gt; select x from numbers order by x limit 5 offset 0;
+----+
| x  |
+----+
| 1  |
| 2  |
| 3  |
| 4  |
| 5  |
+----+
[localhost:21000] &gt; select x from numbers order by x limit 5 offset 5;
+----+
| x  |
+----+
| 6  |
| 7  |
| 8  |
| 9  |
| 10 |
+----+
</codeblock>
  </conbody>
</concept>