Beginning Oracle Database 11g Administration From Novice to Professional

CHAPTER 7 PHYSICAL DATABASE DESIGN 135
for example, no two employees can share a social security number. This is particularly
true of any column or combination of columns designated as a primary key.
foreign keys. A foreign key is a column or set
of columns that is required to map to the primary key of another table. Full table
scans and table- level locks can result if a foreign key is not indexed. 1
Oracle Database 11g provides several “advisors” that can generate recommendations
for improving the performance of SQL queries; I will discuss them in detail in Chapter 17,
which covers SQL tuning. Listing 7-1 provides an example of how the procedure
can be used to analyze an SQL statement and determine if additional indexes
would improve performance. In this case, the procedure recommends that
a “function- based index” be created and even provides the necessary SQL commands to
do so; you can replace the system- generated name for the index with a more meaningful
name. Note that you need the privilege in order to use the procedure.
Listing 7-1. Using the Procedure to Analyze an SQL Query and Determine if Additional
Indexes Should Be Created to Improve Performance
1. In Expert One-On-One Oracle, Tom Kyte says: “I sometimes wish I had a dollar for every time I was able
to solve the insolvable hanging issue by simply running the query to detect un- indexed foreign keys and
suggesting that we index the one causing the problem—I would be very rich.” Tom provides the script in
the book—it can also be found at .