SQL query: Simulating an “AND” over several rows instead of sub-querying

Question

Suppose I have a \"tags\" table with two columns: tagid and contentid. Each row represents a tag assigned to a piece of content. I want a

Answer 1

What type of SQL? MS SQL Server, Oracle, MySQL?

In SQL Server doesn't this equate to:

select contentid from tags where tagid IN (334,338,342)