So sometimes you’re digging through a table and there isn’t an obvious primary key (normally Number). While most of the tables this happens on aren’t usually exported but in case you need to, you can query the table for the primary key by using this projection, then you can hopefully figure out what the key is named.
<quer:projection alias="Validkey" xmlns:quer="http://www.taleo.com/ws/integration/query">
<quer:key path=""/>
</quer:projection>