The relationships between columns in different tables are typically described through the use of keys, which are implemented through referential integrity constraints and their supporting indexes. For example, in Figure 1-2, you can establish a link between the DEPTNO column in the second table, which is called a foreign key,to the DEPTNO column in the first table, which is referred to as the primary key of that table. Finally, even if you define many different indexes for a table, you don’t have to understand them or manage the data they contain. Oracle includes a query optimizer (described in Chapter 4) that chooses the best way to use your.
