Here are some of the articles on Queries and related query/SQL programming. At the top of each article you will see which collection (gold, silver or bronze) the article belongs to.
Consolidating Your Data With Queries
Simplifying Complex SQL
Access Answers: All in the Family
Tame the Crosstab Missing Column Beast
Computing the Median (Again)
Give Me a Call
Access Subquery Techniques
The full collections and related download files can be purchased here.
Plus these articles on queries