Relationship between t-Sql and "Set Theory"

I have always heard that much of t-sql is based on "set theory". I had Set theory in high school and I remember it as being simple Unions, Intersections, Differences of Sets. By a Set I mean a collection such as {2,5,7,8,9, ...) That could well described a single row in a table. By unioning several of these rows we could end up with a table.

But how does that relate to t-sql such as

select * from <table name> Where <condition 1> ?

Is it simply that the result returned by the query is a Set? (if so, a Set is simply being used as a synonym for a Collection. No set theory involved.)

TIA,

barkingdog

This is quite a large subject =;o)

Perhaps the best way is to point you to some reading, to get you started.
http://en.wikipedia.org/wiki/Relational_model

/Kenneth