SQL Check one list against Another
<p>I'd appreciate any pointers on how in SQL to check whether elements in one list also appear in another.</p>

<pre><code>List A = Live Customers in April
List B = Live Customers in May
</code></pre>

<p>How can I check which Customers in List A also appear in List B ? to identify those Customers which have been lost </p>

<pre><code>i.e. Customers in A but not in B.
</code></pre>

<p>Thank you for your help. Gav</p>