6. Stage 4--Optimize the Database Schema : Performance Considerations : Using Foreign Key Specifications
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Using Foreign Key Specifications
Specifying primary and foreign key constraints provide the optimizer with more information about the structure of data and in some cases can improve query performance.
Such constraints are typically enforced by VectorH generating secondary indexes, and these in turn may degrade performance. However, VectorH also provides a mechanism whereby such constraints can be declared as NOT ENFORCED. This type of constraint can often help third-party tools generate “better” SQL and in turn provide better query execution. As the name implies, however, such constraints are not enforced, meaning that the actual data may not conform to the constraint.