SQL: How to check if all IDs in a list are in a table
<p>first of all I am sorry if this question is too obvious, since I am quite new in SQL.</p>

<p>So, I have a list of IDs (variable, depending how many products the user chooses). And I want to check if all of them are in a table. If one of them is not, the result of the query should be null. If all of them are there, the result should be all the rows where those IDs are. </p>

<p>How can I do this?</p>

<p>Best regards,
Flavio</p>