<div id="docs-body">
 <div class="section">
  <div class="titlepage">
   <div>
    <div>
     <h4 class="title">
      <a name="working-with-null">
      </a>
      5.3.4.6 Working with NULL Values
     </h4>
    </div>
   </div>
  </div>
  <a class="indexterm" name="idm46045325110000">
  </a>
  <a class="indexterm" name="idm46045325108960">
  </a>
  <p>
   The
   <code class="literal">
    NULL
   </code>
   value can be surprising until you
          get used to it. Conceptually,
   <code class="literal">
    NULL
   </code>
   means
   <span class="quote">
    “
    <span class="quote">
     a missing unknown value
    </span>
    ”
   </span>
   and it is treated
          somewhat differently from other values.
  </p>
  <p>
   To test for
   <code class="literal">
    NULL
   </code>
   , use the
   <a class="link" href="comparison-operators.html#operator_is-null">
    <code class="literal">
     IS NULL
    </code>
   </a>
   and
   <a class="link" href="comparison-operators.html#operator_is-not-null">
    <code class="literal">
     IS
          NOT NULL
    </code>
   </a>
   operators, as shown here:
  </p>
  <div class="copytoclipboard-wrapper">
   <pre class="programlisting language-sql"><div class="docs-select-all right" id="sa95153330"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql&gt;</span> <span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token operator">IS</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token operator">IS</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 IS NULL <span class="token punctuation">|</span> 1 IS NOT NULL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span>         0 <span class="token punctuation">|</span>             1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
  </div>
  <p>
   You cannot use arithmetic comparison operators such as
   <a class="link" href="comparison-operators.html#operator_equal">
    <code class="literal">
     =
    </code>
   </a>
   ,
   <a class="link" href="comparison-operators.html#operator_less-than">
    <code class="literal">
     &lt;
    </code>
   </a>
   , or
   <a class="link" href="comparison-operators.html#operator_not-equal">
    <code class="literal">
     &lt;&gt;
    </code>
   </a>
   to
          test for
   <code class="literal">
    NULL
   </code>
   . To demonstrate this for
          yourself, try the following query:
  </p>
  <div class="copytoclipboard-wrapper">
   <pre class="programlisting language-sql"><div class="docs-select-all right" id="sa49655246"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql&gt;</span> <span class="token keyword">SELECT</span> <span class="token number">1</span> <span class="token operator">=</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token operator">&lt;&gt;</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token operator">&lt;</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token number">1</span> <span class="token operator">&gt;</span> <span class="token boolean">NULL</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 1 = NULL <span class="token punctuation">|</span> 1 &lt;&gt; NULL <span class="token punctuation">|</span> 1 &lt; NULL <span class="token punctuation">|</span> 1 &gt; NULL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span>     NULL <span class="token punctuation">|</span>      NULL <span class="token punctuation">|</span>     NULL <span class="token punctuation">|</span>     NULL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
  </div>
  <p>
   Because the result of any arithmetic comparison with
   <code class="literal">
    NULL
   </code>
   is also
   <code class="literal">
    NULL
   </code>
   , you
          cannot obtain any meaningful results from such comparisons.
  </p>
  <p>
   In MySQL,
   <code class="literal">
    0
   </code>
   or
   <code class="literal">
    NULL
   </code>
   means false and anything else means true. The default truth
          value from a boolean operation is
   <code class="literal">
    1
   </code>
   .
  </p>
  <p>
   This special treatment of
   <code class="literal">
    NULL
   </code>
   is why, in
          the previous section, it was necessary to determine which
          animals are no longer alive using
   <code class="literal">
    death IS NOT
          NULL
   </code>
   instead of
   <code class="literal">
    death &lt;&gt;
          NULL
   </code>
   .
  </p>
  <p>
   Two
   <code class="literal">
    NULL
   </code>
   values are regarded as equal in a
   <code class="literal">
    GROUP BY
   </code>
   .
  </p>
  <p>
   When doing an
   <code class="literal">
    ORDER BY
   </code>
   ,
   <code class="literal">
    NULL
   </code>
   values are presented first if you do
   <code class="literal">
    ORDER BY ... ASC
   </code>
   and last if you do
   <code class="literal">
    ORDER BY ... DESC
   </code>
   .
  </p>
  <p>
   A common error when working with
   <code class="literal">
    NULL
   </code>
   is to
          assume that it is not possible to insert a zero or an empty
          string into a column defined as
   <code class="literal">
    NOT NULL
   </code>
   ,
          but this is not the case. These are in fact values, whereas
   <code class="literal">
    NULL
   </code>
   means
   <span class="quote">
    “
    <span class="quote">
     not having a
          value.
    </span>
    ”
   </span>
   You can test this easily enough by using
   <code class="literal">
    IS [NOT] NULL
   </code>
   as shown:
  </p>
  <div class="copytoclipboard-wrapper">
   <pre class="programlisting language-sql"><div class="docs-select-all right" id="sa6959649"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-sql"><span class="token prompt">mysql&gt;</span> <span class="token keyword">SELECT</span> <span class="token number">0</span> <span class="token operator">IS</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token number">0</span> <span class="token operator">IS</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token string">''</span> <span class="token operator">IS</span> <span class="token boolean">NULL</span><span class="token punctuation">,</span> <span class="token string">''</span> <span class="token operator">IS</span> <span class="token operator">NOT</span> <span class="token boolean">NULL</span><span class="token punctuation">;</span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span> 0 IS NULL <span class="token punctuation">|</span> 0 IS NOT NULL <span class="token punctuation">|</span> '' IS NULL <span class="token punctuation">|</span> '' IS NOT NULL <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span>
<span class="token output"><span class="token punctuation">|</span>         0 <span class="token punctuation">|</span>             1 <span class="token punctuation">|</span>          0 <span class="token punctuation">|</span>              1 <span class="token punctuation">|</span></span>
<span class="token output"><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">-</span><span class="token punctuation">+</span></span></code></pre>
  </div>
  <p>
   Thus it is entirely possible to insert a zero or empty string
          into a
   <code class="literal">
    NOT NULL
   </code>
   column, as these are in
          fact
   <code class="literal">
    NOT NULL
   </code>
   . See
   <a class="xref" href="problems-with-null.html" title="B.3.4.3 Problems with NULL Values">
    Section B.3.4.3, “Problems with NULL Values”
   </a>
   .
  </p>
 </div>
 <br/>
</div>
