Query Containment

[PeterFranko]

Hi guys, I need your help, please.

Is "Query Containment" the same as "Nested Query"? If not, could you give me an easy example of what "Query Containment" is?

Thank you. Peter

[SpywareDr]

Any help here? https://courses.cs.washington.edu/co...ve-queries.pdf

[PeterFranko]

Hi SpywareDr,
this is a really great lecture, thank you. However, it is written in such a technical language, that I was really struggling to understand. Somehow at the end I still do not know the answer. The problem is that we were given a small task:
"Show a practical example of query containment." And my colleagues started giving examples of nested queries and SELECT inside another SELECT. Now I have a feeling that these topics are not related and that my colleagues are wrong. Are they? Or maybe me?
Tank you. Peter.

[SpywareDr]

Encyclopedia of Database systems > Query Containment

Definition

One query is contained in another if, independent of the values of the “stored data” (that is, database), the set of answers to the first query on the database is a subset of the set of answers to the second query on the same database.

A formal definition of containment is as follows: [...continues...]