The mother of all interviews

On Thursday, I interviewed someone for a contracting position in my project. I was going through the routine and didn't find his communication to be good. His process knowledge wasn't that great either. I anyway had to evaluate his technical ability as well. Looking through his resume, I found that he had listed Oracle and SQL Server. Since my project involves quite a good amount of querying, I decided to evaluate him on that.
I have done my best to recollect the exact conversation the two of us had, but you will anyway get the idea....
me: So ..., you have mentioned Oracle and SQL Server in your resume
him: Yeah.....I know Oracle and SQL
me: Great. So how comfortable are you in it?
him: Yeah... I know Oracle and SQL
me: Ok, so you are okay with SQL Queries?
him: Yeah.. I have written queries in my previous project.
me: Good. So where would you rate yourself with respect to SQL Queries?
him: I am not getting the question
me: Where would you rate yourself on SQL Queries?
him: I don't understand your question
me: You said you know Oracle and SQL..
him: Yeah I know Oracle and SQL
me: Yes, and you also said you have written queries in your previous project
him: Yeah, I have written queries
me: So, I am asking you to rate yourself with respect to SQL Queries
him: I still don't get your question
[Note: The line is very clear. No disturbance. I have a very loud voice.]
me: Can you please rate yourself on SQL Queries? On a scale of 1 to 5, 5 being the highest?
him:
me: Hello..
him: Yes, I cant understand your question
me: I am just asking you to do a self-rating of your capability with respect to SQL Query
him: I don't know
me: Just give a rank to yourself. Like grades..
him: Sorry, I don't know the answer to the question
me: You said you know Oracle and SQL. You said you have used SQL Queries. So I just want to find out where you would rate or rank or grade yourself, on a scale of 1 to 5?
him: I cant understand your question
me: "xyz"(his name), I am only asking you to rate yourself on a scale of 1 to 5. If you rate yourself as 5/5 it means you have exceptional knowledge. If its 4/5 it means that you are above average. So on and so forth. Now, will you please rate yourself on SQL Queries?
him: I don't know the answer. Can we skip this question?

At about this time, I was planning on shouting at him or breaking the phone. Both of which, would have been detrimental to my career.
However, since I was representing my Company, I still had to finish the conversation on proper terms and so my response was "If I ask you questions on SQL Queries, will you be able to answer them?". He replied in the affirmative. But it was a different deal that he couldn't get past the basic ones itself.

Needless to add, I didn't select the candidate. And even more importantly, I didn't even say the formal "Nice talking to you".