Why Informational Constraints?
DB2 UDB introduced support for constraint checking in the DB2 Common Server version 2 release. Both check constraints and referential integrity constraints were included and used to enforce business logic and schema rules in the database.
Constraints are really used for two purposes:
Ensuring the integrity of the database and its data.
Enhancing the performance for query workloads.
Query performance improvements as a result of defining constraints in the database were introduced in DB2 UDB version 6. The ability to use constraints as a performance enhancer comes from the integration of check and referential integrity constraints into the query graph model (QGM). This integration gives the DB2 UDB optimizer more information ...
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