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<title>5.2. Comparison Functions and Operators — Presto 0.104 Documentation</title>
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<div class="header">
<h1 class="heading"><a href="../index.html">
<span>Presto 0.104 Documentation</span></a></h1>
<h2 class="heading"><span>5.2. Comparison Functions and Operators</span></h2>
</div>
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<div class="section" id="comparison-functions-and-operators">
<h1>5.2. Comparison Functions and Operators</h1>
<div class="section" id="comparison-operators">
<h2>Comparison Operators</h2>
<table border="1" class="docutils">
<colgroup>
<col width="16%" />
<col width="84%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Operator</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><tt class="docutils literal"><span class="pre"><</span></tt></td>
<td>Less than</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">></span></tt></td>
<td>Greater than</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre"><=</span></tt></td>
<td>Less than or equal to</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">>=</span></tt></td>
<td>Greater than or equal to</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">=</span></tt></td>
<td>Equal</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre"><></span></tt></td>
<td>Not equal</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">!=</span></tt></td>
<td>Not equal (non-standard but popular syntax)</td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="range-operator-between">
<h2>Range Operator: BETWEEN</h2>
<p>The <tt class="docutils literal"><span class="pre">BETWEEN</span></tt> operator tests if a value is within a specified range.
It uses the syntax <tt class="docutils literal"><span class="pre">value</span> <span class="pre">BETWEEN</span> <span class="pre">min</span> <span class="pre">AND</span> <span class="pre">max</span></tt>:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="mi">3</span> <span class="k">BETWEEN</span> <span class="mi">2</span> <span class="k">AND</span> <span class="mi">6</span><span class="p">;</span>
</pre></div>
</div>
<p>The statement shown above is equivalent to the following statement:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="mi">3</span> <span class="o">>=</span> <span class="mi">2</span> <span class="k">AND</span> <span class="mi">3</span> <span class="o"><=</span> <span class="mi">6</span><span class="p">;</span>
</pre></div>
</div>
<p>To test if a value does not fall within the specified range
use <tt class="docutils literal"><span class="pre">NOT</span> <span class="pre">BETWEEN</span></tt>:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="mi">3</span> <span class="k">NOT</span> <span class="k">BETWEEN</span> <span class="mi">2</span> <span class="k">AND</span> <span class="mi">6</span><span class="p">;</span>
</pre></div>
</div>
<p>The statement shown above is equivalent to the following statement:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="mi">3</span> <span class="o"><</span> <span class="mi">2</span> <span class="k">OR</span> <span class="mi">3</span> <span class="o">></span> <span class="mi">6</span><span class="p">;</span>
</pre></div>
</div>
<p>The presence of NULL in a <tt class="docutils literal"><span class="pre">BETWEEN</span></tt> or <tt class="docutils literal"><span class="pre">NOT</span> <span class="pre">BETWEEN</span></tt> statement
will result in the statement evaluating to NULL:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="k">NULL</span> <span class="k">BETWEEN</span> <span class="mi">2</span> <span class="k">AND</span> <span class="mi">4</span><span class="p">;</span> <span class="o">=></span> <span class="k">null</span>
<span class="k">SELECT</span> <span class="mi">2</span> <span class="k">BETWEEN</span> <span class="k">NULL</span> <span class="k">AND</span> <span class="mi">6</span><span class="p">;</span> <span class="o">=></span> <span class="k">null</span>
</pre></div>
</div>
<p>The <tt class="docutils literal"><span class="pre">BETWEEN</span></tt> and <tt class="docutils literal"><span class="pre">NOT</span> <span class="pre">BETWEEN</span></tt> operators can also be used to
evaluate string arguments:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="s1">'Paul'</span> <span class="k">BETWEEN</span> <span class="s1">'John'</span> <span class="k">AND</span> <span class="s1">'Ringo'</span><span class="p">;</span> <span class="o">=></span> <span class="k">true</span>
</pre></div>
</div>
<p>Not that the value, min, and max parameters to <tt class="docutils literal"><span class="pre">BETWEEN</span></tt> and <tt class="docutils literal"><span class="pre">NOT</span>
<span class="pre">BETWEEN</span></tt> must be the same type. For example, Presto will produce an
error if you ask it if John is between 2.3 and 35.2.</p>
</div>
<div class="section" id="is-null-and-is-not-null">
<h2>IS NULL and IS NOT NULL</h2>
<p>The <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">NULL</span></tt> and <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">NOT</span> <span class="pre">NULL</span></tt> operators test whether a value
is null (undefined). Both operators work for all data types.</p>
<p>Using <tt class="docutils literal"><span class="pre">NULL</span></tt> with <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">NULL</span></tt> evaluates to true:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">select</span> <span class="k">NULL</span> <span class="k">IS</span> <span class="k">NULL</span><span class="p">;</span> <span class="o">=></span> <span class="k">true</span>
</pre></div>
</div>
<p>But any other constant does not:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="mi">3</span><span class="p">.</span><span class="mi">0</span> <span class="k">IS</span> <span class="k">NULL</span><span class="p">;</span> <span class="o">=></span> <span class="k">false</span>
</pre></div>
</div>
</div>
<div class="section" id="is-distinct-from-and-is-not-distinct-from">
<h2>IS DISTINCT FROM and IS NOT DISTINCT FROM</h2>
<p>In SQL a <tt class="docutils literal"><span class="pre">NULL</span></tt> value signifies an unknown value, so any comparison
involving a <tt class="docutils literal"><span class="pre">NULL</span></tt> will produce <tt class="docutils literal"><span class="pre">NULL</span></tt>. The <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">DISTINCT</span> <span class="pre">FROM</span></tt>
and <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">NOT</span> <span class="pre">DISTINCT</span> <span class="pre">FROM</span></tt> operators treat <tt class="docutils literal"><span class="pre">NULL</span></tt> as a known value
and both operators guarantee either a true or false outcome even in
the presence of <tt class="docutils literal"><span class="pre">NULL</span></tt> input:</p>
<div class="highlight-sql"><div class="highlight"><pre><span class="k">SELECT</span> <span class="k">NULL</span> <span class="k">IS</span> <span class="k">DISTINCT</span> <span class="k">FROM</span> <span class="k">NULL</span><span class="p">;</span> <span class="o">=></span> <span class="k">false</span>
<span class="k">SELECT</span> <span class="k">NULL</span> <span class="k">IS</span> <span class="k">NOT</span> <span class="k">DISTINCT</span> <span class="k">FROM</span> <span class="k">NULL</span><span class="p">;</span> <span class="o">=></span> <span class="k">true</span>
</pre></div>
</div>
<p>In the example shown above, a <tt class="docutils literal"><span class="pre">NULL</span></tt> value is not considered
distinct from <tt class="docutils literal"><span class="pre">NULL</span></tt>. When you are comparing values which may
include <tt class="docutils literal"><span class="pre">NULL</span></tt> use these operators to guarantee either a <tt class="docutils literal"><span class="pre">TRUE</span></tt> or
<tt class="docutils literal"><span class="pre">FALSE</span></tt> result.</p>
<p>The following truth table demonstrate the handling of <tt class="docutils literal"><span class="pre">NULL</span></tt> in
<tt class="docutils literal"><span class="pre">IS</span> <span class="pre">DISTINCT</span> <span class="pre">FROM</span></tt> and <tt class="docutils literal"><span class="pre">IS</span> <span class="pre">NOT</span> <span class="pre">DISTINCT</span> <span class="pre">FROM</span></tt>:</p>
<table border="1" class="docutils">
<colgroup>
<col width="13%" />
<col width="13%" />
<col width="15%" />
<col width="15%" />
<col width="19%" />
<col width="26%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">a</th>
<th class="head">b</th>
<th class="head">a = a</th>
<th class="head">a <> b</th>
<th class="head">a DISTINCT b</th>
<th class="head">a NOT DISTINCT b</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">1</span></tt></td>
<td><tt class="docutils literal"><span class="pre">1</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">1</span></tt></td>
<td><tt class="docutils literal"><span class="pre">2</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">1</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">NULL</span></tt></td>
<td><tt class="docutils literal"><span class="pre">FALSE</span></tt></td>
<td><tt class="docutils literal"><span class="pre">TRUE</span></tt></td>
</tr>
</tbody>
</table>
</div>
<div class="section" id="greatest-and-least">
<h2>GREATEST and LEAST</h2>
<p>These functions are not in the SQL standard, but are a common extension.
Like most other functions in Presto, they return null if any argument is
null. Note that in some other databases, such as PostgreSQL, they only
return null if all arguments are null.</p>
<p>The following types are supported:
<tt class="docutils literal"><span class="pre">DOUBLE</span></tt>,
<tt class="docutils literal"><span class="pre">BIGINT</span></tt>,
<tt class="docutils literal"><span class="pre">VARCHAR</span></tt>,
<tt class="docutils literal"><span class="pre">TIMESTAMP</span></tt>,
<tt class="docutils literal"><span class="pre">TIMESTAMP</span> <span class="pre">WITH</span> <span class="pre">TIME</span> <span class="pre">ZONE</span></tt>,
<tt class="docutils literal"><span class="pre">DATE</span></tt></p>
<dl class="function">
<dt id="greatest">
<tt class="descname">greatest</tt><big>(</big><em>value1</em>, <em>value2</em><big>)</big> → [same as input]</dt>
<dd><p>Returns the largest of the provided values.</p>
</dd></dl>
<dl class="function">
<dt id="least">
<tt class="descname">least</tt><big>(</big><em>value1</em>, <em>value2</em><big>)</big> → [same as input]</dt>
<dd><p>Returns the smallest of the provided values.</p>
</dd></dl>
</div>
</div>
</div>
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