SQL GROUP BY and Functional Dependencies: A Very Useful Feature

Relational databases define the term "Functional Dependency" as such (from Wikipedia): In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. In other words, functional dependency is a constraint that describes the relationship between attributes in a relation. In SQL, functional dependencies appear whenever … Continue reading SQL GROUP BY and Functional Dependencies: A Very Useful Feature

Subtle SQL differences: Constraint names

The various SQL product vendors implement subtle differences in the way they interpret SQL. In this case, I've been examining the reuse of constraint names within a schema / database (which is yet another story: what's a schema, what's a database?). Here's the summary: Constraint names are unique within a schema Derby H2 HSQLDB Ingres … Continue reading Subtle SQL differences: Constraint names