I'm quite surprised by all the answers in tune of "It depends on the story".
To me, it seems that that is exactly what the OP is asking about: given no mechanical/timing limitations, how combat-intensive stories would you like to play? And that is what I answered. While there are many types of stories I like in a game, on average two combats in a 6-7h session is fine for me.
There are two problems with the question, "How combat-intensive stories would you like to play?"
The first is related directly to the question. The answer to such a question can only be, "It depends. I like all kinds. Tell me a good story." And also, the amount of combat in a session isn't entirely up to the DM. If I'm playing a character who tends to try to solve problems by hitting them with something sharp, we'll tend to have more combat heavy sessions than if the PC's all tend to look for alternative solutions.
The second problem is related to the way the player asked the question. The player stated his question in terms of a 'session' which is an arbitrary portion of the story. I don't and don't think I can structure events around a session. Unless I'm specifically writing a tournament type scenario with limited choices and no expectation of roleplaying, I never know how much material a session is going to consume. A session is not a 'chapter', 'scene', or 'story'. It's just a period of time that we happen to be telling the story together. In such a period of time, how many combats you have depends on what sort of story you are telling and on whether you are in a combat heavy portion of the story. If that session occurs within a part of the story heavy on roleplay, investigation, or intrigue then '0-1' is probably the answer I'll give for how many combats should occur in the session. If that session occurs within a battle, the exploration of some monster rich area, or something of that sort, then 'as many as we can fit in' might be a better expectation. In which case, practically the answer is 'about 8', but if we could do them in 2 minutes consistantly it might be 20 or more. And I can't answer this by taking an average either. There isn't a rule that says, "You need 1 combat heavy session every other session.", or anything of that nature.
As I said, I've gone several sessions without combat and been happy about it. And I've been in sessions where the combat essentially didn't stop the whole session long.