Chapter 3 PHYSICAL DATABASE DESIGN AND IMPLEMENTATION 155
Chapter 3 PHYSICAL DATABASE DESIGN AND IMPLEMENTATION 155 When an INSERT operation is performed on a table, you must supply values for all columns that do not have a default entry defined or that allow NULL content. Application of Integrity Options As discussed throughout this chapter, a number of techniques are available to maintain the integrity of the database. Each of these techniques will in part provide a usable, responsive system that prevents inappropriate data from getting into the system. Table 3.1 summarizes these techniques and provides some further detail as to what can be expected in their use. TABLE 3.1 INTEGRITY MAINTENANCE OBJECTS Technique Integrity Achieved Usage Timing (Log) Primary Key Entity Identify each row Before Foreign Key Referential/Domain Ensure no orphan child elements Before Unique Index Entity Ensure entries are exclusive Before Unique Constraint Entity No duplicate column values Before Identity Entity Auto-incremented values Before Check Constraint Domain Ensure correct column entry Before Not NULL Domain A value must be present Before Default Domain Provides initial value Before Rule Domain Ensure correct column entry Before Trigger Referential/Domain Respond to add, change, delete After Stored Procedures Referential/Domain/ Entity Process-controlled operations Before
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