subquery (nested query) SQL design - please recommend good sites (1 Viewer)

Does anyone have any good tutorials or references for subquery designs?
Some Crosstab and Summary queries using subqueries examples or guidlines would also be useful.

I am a little rusty after not doing this for awhile and need to get much more efficient to convert a handfull of these.

My designs have included creating a query, then having a second (or third) query call on the other queries or (cross tab queries).
They work as intended, but should probably be combined into vba code as shown in the msdn example below.


A subquery is a SELECT statement nested inside a SELECT, SELECT…INTO, INSERT…INTO, DELETE, or UPDATE statement or inside another subquery.

Here is an example of one using VBA code:
http://msdn.microsoft.com/en-us/library/bb208942(v=office.12).aspx

Thank you, very useful.
And, this site also reminded me of the term Correlated Subquery.