Jennifer Widom Constraints Triggers Motivation and overview Jennifer Widom 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 structure and types Examples Jennifer Widom 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 structure and types Classification Jennifer Widom Constraints Triggers Declaring and enforcing constraints Declaration With original schema Or later Enforcement Check after every modification Deferred constraint checking Jennifer Widom Constraints Triggers Triggers “EventConditionAction Rules” When event occurs, check condition; if true, do action Examples Jennifer Widom Constraints Triggers Triggers “EventConditionAction Rules” When event occurs, check condition; if true, do action Why use them? Jennifer Widom Constraints Triggers Triggers in SQL “EventConditionAction Rules” Create Trigger name Before|After|Instead Of events referencingvariables For Each Row When ( condition ) action Jennifer Widom 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
Trang 1Constraints & Triggers
Motivation and
overview
Trang 2Jennifer Widom
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
Trang 3Integrity Constraints
Impose restrictions on allowable data, beyond those
imposed by structure and types
Examples
Trang 4Jennifer Widom
Constraints & Triggers
Integrity Constraints
Impose restrictions on allowable data, beyond those
imposed by structure and types
Why use them?
Trang 5Integrity Constraints
Impose restrictions on allowable data, beyond those
imposed by structure and types
Classification
Trang 6Jennifer Widom
Constraints & Triggers
Declaring and enforcing constraints
Declaration
With original schema
Or later
Enforcement
Check after every modification
Deferred constraint checking
Trang 7Triggers
“Event-Condition-Action Rules”
When event occurs, check condition; if true, do action
Examples
Trang 8Jennifer Widom
Constraints & Triggers
Triggers
“Event-Condition-Action Rules”
When event occurs, check condition; if true, do action
Why use them?
Trang 9Triggers in SQL
“Event-Condition-Action Rules”
Create Trigger name
Before|After|Instead Of events
[ referencing-variables ]
action
Trang 10Jennifer Widom
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