Sorry, that wasn't very clear. I meant the sandbox provided in the learning labs.

Is this app supposed to be tested from the Sandbox you provide ?

Both tables belong to the same namespace TEST_NAMESPACE.

Is there a chance this raises an error because of the content of the strings in one of the columns ? E.g : if the string is too long (though it's capped to max length 2000) or special characters are in it (like single quotes that might interfere with SQL queries).