Constraints Triggers Motivation and overview Jennifer Widom Constraints

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Constraints & Triggers Motivation and overview Jennifer Widom

Constraints & Triggers Motivation and overview Jennifer Widom

Constraints & Triggers Constraints and Triggers § For relational databases § SQL standard; systems

Constraints & Triggers Constraints and Triggers § For relational databases § SQL standard; systems vary considerably (Integrity) Constraints constrain allowable database states Triggers monitor database changes, check conditions and initiate actions Jennifer Widom

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by structure and types Examples Jennifer Widom

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by structure and types Why use them? Jennifer Widom

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by

Constraints & Triggers Integrity Constraints Impose restrictions on allowable data, beyond those imposed by structure and types Classification Jennifer Widom

Declaring and enforcing constraints Declaration § With original schema Constraints & Triggers § Or

Declaring and enforcing constraints Declaration § With original schema Constraints & Triggers § Or later Enforcement § Check after every modification § Deferred constraint checking Jennifer Widom

Constraints & Triggers “Event-Condition-Action Rules” When event occurs, check condition; if true, do action

Constraints & Triggers “Event-Condition-Action Rules” When event occurs, check condition; if true, do action Examples Jennifer Widom

Constraints & Triggers “Event-Condition-Action Rules” When event occurs, check condition; if true, do action

Constraints & Triggers “Event-Condition-Action Rules” When event occurs, check condition; if true, do action Why use them? Jennifer Widom

Triggers in SQL “Event-Condition-Action Rules” Constraints & Triggers Create Trigger name Before|After|Instead Of events

Triggers in SQL “Event-Condition-Action Rules” Constraints & Triggers Create Trigger name Before|After|Instead Of events [ referencing-variables ] [ For Each Row ] When ( condition ) action Jennifer Widom

Constraints & Triggers Constraints and Triggers § For relational databases § SQL standard; systems

Constraints & Triggers Constraints and Triggers § For relational databases § SQL standard; systems vary considerably (Integrity) Constraints constrain allowable database states Triggers monitor database changes, check conditions and initiate actions Jennifer Widom

Constraints Triggers Introduction Jennifer Widom Triggers EventConditionAction RulesConstraints Triggers Introduction Jennifer Widom Triggers EventConditionAction Rules
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