
184 7.2 How Oracle SQL Is Executed
Nested Subquery Semi-Joins. As already mentioned earlier in this
chapter, it is possible to tune joins or at least simplify their coding, by
using nested layers of subqueries. However, this type of tuning is
more likely to apply in highly normalized OLTP transaction data
model structures, not data warehouse data models.
7.2 How Oracle SQL Is Executed
What happens when an Oracle SQL statement is sent to the database? A
portion of memory is allocated to store the results of a SQL statement. This
chunk of memory is called a cursor. Among other things, a cursor contains
a pointer to the row in an index or table currently ...