I just finished reading a chapter in my study guide that seemed to cover the whole Oracle database. It went over constraints, indexes, sequences, synonyms, procedures, functions, packages, triggers, and the Data Dictionary.Primary key constraints incorporate NOT NULL constraints and unique constraints. Oracle implements a "Match None rule" for foreign key constraints. That is, if any column that a FK constraint is on turns out to be NULL, the database does not enforce the other columns to have to match the primary key values.
The default behavior with the help of indexes is a full table scan. A B-Tree index is the default type. It provides the best performance for columns with many distinct values (i.e. high cardinality). Bitmap indexes are better for columns with low cardinality. In addition, they only add value if Oracle can use a lot of them to limit the rows searched.
