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Events and Active Concepts in Database Systems

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Events and Active Concepts in Database Systems EventsEvents andand activeactive conceptsconcepts inin databasedatabase systemssystems Trigger in SQL:1999 (Oracle) Active Database systems EventsEvents inin DBS:DBS: MotivationMotivation Assumption: Data stored in DB Architectures: New book 1.Alternative Amazon Web-interface ? DB DBMS Application ! 2.Alternative New book FU-Berlin, DBS I 2006, Amazon Web-interface DB DBMS Application Hinze / Scholz / Hinze ENS 7.2 EventsEvents inin DBS:DBS: MotivationMotivation Idea: Active Database System (ADBS) New book Application DB aDBMS FU-Berlin, DBS I 2006, Active database — Relational or object oriented data base — Triggers actions in reaction on (system)events Hinze / Scholz / Hinze — ECA-Rules specify event, condition, action 7.3 EventsEvents inin DBS:DBS: Conceivable events: — Database state transitions — Temporal events — Abstract or external events Examples: — Relational: (Sybase, Ingres) — Object-relational: Postgres — Object-oriented: Sentinel, Ode [agr89], Samos[dit00] FU-Berlin, DBS I 2006, Simple triggers also in SQL:1999 (Oracle) Hinze / Scholz / Hinze 7.4 EventsEvents inin DBS:DBS: Argumentation for aDBS: — central management of semantic in DB — optimization of processing — higher DBMS functionality — support of time-dependent requirements Typical applications: — monitoring of integrity constraints — access control — service for derived data within database (view update) FU-Berlin, DBS I 2006, — but also: trigger of external actions (notify administrator about weird actions on data) Hinze / Scholz / Hinze 7.5 EventsEvents inin DBS:DBS: RoadmapRoadmap Trigger in SQL:1999 — Standard —Example: Oracle Active Database Systems FU-Berlin, DBS I 2006, Hinze / Scholz / Hinze 7.6 Trigger in SQL1999: Introduction Simplified integrity rules Simple conditions CREATE TRIGGER <TriggerName> {before|after } {insert|delete|update} ON <RelationName> [referencing old as <OldName>, new as <NewName>] [WHEN <Condition>] [for each row|statement] <SQLStatement> FU-Berlin, DBS I 2006, — called on insert/update/delete on specified relation — references: binds variables to old/new tuples of a relation — for each row: activates action for all selected tuples Hinze / Scholz / Hinze — for each statement: activates action once for each condition —Only for single table 7.7 Trigger in SQL1999: Trigger Example Example: — count the number of inserted books createcreate triggertrigger BookCountPlusBookCountPlus onon insertinsert onon BookBook referencingreferencing oldold asas OldOld newnew asas NewNew updateupdate BookCountBookCount setset New.NumberNew.Number == Old.Number+1Old.Number+1 forfor eacheach rowrow createcreate triggertrigger BookCountMinusBookCountMinus FU-Berlin, DBS I 2006, ...... setset New.NumberNew.Number == Old.Number-1Old.Number-1 Hinze / Scholz / Hinze 7.8 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger ExampleExample Example: — check that the budget holds — just once per update statement createcreate triggertrigger BudgetTestBudgetTest afterafter updateupdate onon SalarySalary forfor eacheach statementstatement whenwhen (SumSalary(SumSalary > > 200.000)200.000) signalsignal „Budget„Budget overflow!“overflow!“ FU-Berlin, DBS I 2006, Note: SumSalary is a function that has been predefined and is just used here Hinze / Scholz / Hinze 7.9 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle — similar to stored procedures — written in PL/SQL, Java (stored internally), or C (stored externally) PL/SQL Block Structure: Stored procedure example: DECLARE – Optional DECLARE Variables, cursors, v_variable VARCHAR2(5); user-defined exceptions BEGIN BEGIN – Mandatory SELECT column_name SQL statements INTO v_variable PL/SQL statements FROM table_name; EXCEPTION – Optional EXCEPTION Actions to perform when WHEN exception_name THEN FU-Berlin, DBS I 2006, errors occur ... END; – Mandatory END; PL/SQL variable Hinze / Scholz / Hinze Bind variable: declared in host environment (e.g.SQL*Plus), 7.10 reference in PL/SQL: :variable TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Supported Events: — DML statements that modify data in a table (INSERT, UPDATE, or DELETE) — DDL statements — System events (startup, shutdown, and error messages) — User events such as logon and logoff Syntax: CREATECREATE [OR[OR REPLACE]REPLACE] TRIGGERTRIGGER <trigger_name><trigger_name> {BEFORE|AFTER|INSTEAD{BEFORE|AFTER|INSTEAD OF}OF} {INSERT|DELETE|UPDATE{INSERT|DELETE|UPDATE [OF[OF column_list]}column_list]} [[REFERENCING[[REFERENCING [NEW[NEW ASAS <new_row_name><new_row_name>]] FU-Berlin, DBS I 2006, [OLD[OLD ASAS <old_row_name><old_row_name>]]]] [FOR[FOR EACHEACH ROWROW [WHEN[WHEN ((condition)]]condition)]] DECLAREDECLARE <<declarations>declarations> BEGINBEGIN Hinze / Scholz / Hinze PL/SQLPL/SQL codecode END;END; 7.11 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Trigger Applications: —Integrity Test — Referential Integrity Test — Event Logging —User Auditing — Maintain table replicas — Gather statistics — Modify tables according to DML statements against views FU-Berlin, DBS I 2006, — Security authorization — Publish events to applications Hinze / Scholz / Hinze 7.12 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Examples of Entity Integrity Triggers CREATECREATE OROR REPLACEREPLACE TRIGGERTRIGGER CUSTOMER_GET_KEYCUSTOMER_GET_KEY BEFOREBEFORE INSERTINSERT ONON CUSTOMERCUSTOMER FORFOR EACHEACH ROWROW DECLAREDECLARE NEW_IDNEW_ID NUMBER;NUMBER; BEGINBEGIN SELECTSELECT MAX(CUSTOMER_ID_NO)MAX(CUSTOMER_ID_NO) INTOINTO NEW_IDNEW_ID FROMFROM CUSTOMER;CUSTOMER; NEW.CUSTOMER_ID_NONEW.CUSTOMER_ID_NO :=:= NEW_IDNEW_ID ++ 1;1; END;END; FU-Berlin, DBS I 2006, CREATECREATE OROR REPLACEREPLACE TRIGGERTRIGGER customer_name_uppercustomer_name_upper BEFOREBEFORE INSERTINSERT OROR UPDATEUPDATE OFOF namename ONON customercustomer FORFOR EACHEACH ROWROW BEGINBEGIN Hinze / Scholz / Hinze :new.name:new.name :=:= UPPER(:new.name)UPPER(:new.name) ;; END;END; 7.13 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Example of a Referential Integrity Trigger CREATECREATE OROR REPLACEREPLACE TRIGTRIGGERGER CUSTOMER_DEL_CHECKCUSTOMER_DEL_CHECK BEFOREBEFORE DELETEDELETE ONON CUSTOMERCUSTOMER FORFOR EACHEACH ROWROW Non-PL/SQL variable DECLAREDECLARE CUSTOMER_COUNTCUSTOMER_COUNT NUMBER;NUMBER; BEGINBEGIN SELECTSELECT COUNT(CUSTOMER_ID_NO)COUNT(CUSTOMER_ID_NO) INTOINTO CUSTOMER_COUNTCUSTOMER_COUNT FROMFROM SALESALE WHEREWHERE CUSTOMER_ID_NOCUSTOMER_ID_NO == :OLD.CUSTOMER_ID_NO;:OLD.CUSTOMER_ID_NO; IFIF (CUSTOMER_COUNT(CUSTOMER_COUNT >> 0)0) THENTHEN FU-Berlin, DBS I 2006, RAISE_APPLICATION_ERROR(-20000,RAISE_APPLICATION_ERROR(-20000, 'Cannot'Cannot deletedelete customercustomer becausebecause itit hashas '||'|| TO_CHAR(CUSTOMER_COUNT,'99999')TO_CHAR(CUSTOMER_COUNT,'99999') |||| '' Sales.');Sales.'); ENDEND IF;IF; END;END; Hinze / Scholz / Hinze 7.14 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Example of a Integrity Constraint Trigger (using exception!) CREATECREATE OROR REPLACEREPLACE TRIGGERTRIGGER pos_cust_balpos_cust_bal BEFOREBEFORE INSERTINSERT OROR UPDATEUPDATE ONON custcust FOR FOR EACHEACH ROWROW DECLAREDECLARE neg_bal_errorneg_bal_error EXCEPTION; EXCEPTION; BEGINBEGIN IFIF :new.balance:new.balance << 00 THENTHEN RAISERAISE neg_bal_errorneg_bal_error ; ; ENDEND IF;IF; EXCEPTIONEXCEPTION FU-Berlin, DBS I 2006, WHENWHEN neg_bal_errorneg_bal_error THEN THEN RAISE_APPLICATION_ERRORRAISE_APPLICATION_ERROR (-20001,(-20001, ‘Negative‘Negative BalBalanceance notnot allowed.’);allowed.’); END;END; Hinze / Scholz / Hinze 7.15 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Triggers vs. integrity constraints: Oracle recommends to use triggers only to enforce: — referential integrity when child and parent tables are on different nodes of a distributed database — complex business rules that are not definable using integrity constraints Reason: FU-Berlin, DBS I 2006, — integrity constrains are “all SQL” - easier, less errors — triggers are more complex to evaluate — Integrity constraints have better performance due to better optimization Hinze / Scholz / Hinze 7.16 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Example of User Auditing Trigger CREATECREATE OROR REPLACEREPLACE TRIGTRIGGERGER audit_cust_triggeraudit_cust_trigger BEFOREBEFORE UPDATEUPDATE ONON custcust FORFOR EACHEACH ROWROW WHENWHEN (new.balance(new.balance <><> old.balance)old.balance) BEGINBEGIN INSERTINSERT INTOINTO audit_custaudit_cust VALUESVALUES (:old.cust_no,(:old.cust_no, :old.name,:old.name, :old.address,:old.address, :old.balance,:old.balance, sysdate);sysdate); END;END; FU-Berlin, DBS I 2006, Hinze / Scholz / Hinze 7.17 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Compiling Triggers: different to PL/SQL blocks PL/SQL block — compiled each time loaded into memory: h1.Syntax checking + parse tree generation h2.Semantic checking: Type checking etc. on the parse tree h3.Code generation(pcode) Trigger — fully compiled at creation time (pcode then stored in the data FU-Berlin, DBS I 2006, dictionary) — firing: no opening of cursor, but direct execution — errors during compilation do not stop trigger creation Hinze / Scholz / Hinze (trigger firing fails + calling action fails) 7.18 TriggerTrigger inin SQL1999SQL1999:: TriggerTrigger inin OracleOracle Modifying Triggers — replace with new definition, or — drop and rerun create trigger Enabling and Disabling Triggers — two modes: enabled (default) / disabled — Enabled: trigger executes
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