Update Cascade Tips Oracle Tips by Burleson Consulting.Mike Ault. August 1.Many times we have the situation.Sql Trigger Update Remote Database' title='Sql Trigger Update Remote Database' />So many frequently Asked interview Questions of Sql and PlSql and so many online tests for Sql and PlSQL.Pl Sql Interview Questions With Answers.Brent Ozar Unlimiteds specialized experts focus on your goals, diagnose your tough database pains, and make Microsoft SQL Server faster and more reliable.Creates a SQL script from the database.SIMPLE does not use multirow insert statements.NODATA will not emit INSERT statements.If the DROP option is specified, drop.Loading DocCommentXchange.Loading DocCommentXchange.In this situation a cascade.Unfortunately Oracle.Corp. doesnt provide this capability in a native manner so a PLSQL.An example of a need for a cascade.For example, there may be two types.If there are dependent tables such as.What would be needed to enforce a.One method would be to utilize data dictionary.However, this may be a lengthy process and.A simpler method would be to implement.The table would contain the.Therefore, the table would.The table DDL script in.If required, a fourth.UPDATETABLES procedure detailed later altered to do an ordered.CREATE TABLE updatetables maintable VARCHAR23.NOT NULL, tablename VARCHAR23.NOT NULL. columnname VARCHAR23.NOT NULL,CONSTRAINT pkupdatetables.PRIMARY KEY maintable,tablename,columnnameUSING INDEXTABLESPACE toolindexesSTORAGE INITIAL 1.K NEXT 1. 00. K PCTINCREASE 0TABLESPACE tools Column definitions are as follows maintable holds the name of the table that the update cascades from.Figure 1 Example DDL to create a cascade update source.The table by itself would be of.Since the data in the table is dynamic i.The. easiest way to do this is to create a set of procedures that.DBMSSQL Oracle provided package to dynamically.Figure 2 shows the commented code for just such a procedure set.The set consists of two procedures, UPDATETABLES and UPDATECOLUMN.First create package body Decided to use package so that all procedures will be in one place and very controllable M.Ault Rev 1. 0 CREATE OR REPLACE PACKAGE cascadeupdate AS First package is updatecolumn This package actually does the work using DBMSSQL to dynamically rebuild the.UPDATEs at run time for each table.PROCEDURE updatecolumn oldvalue IN VARCHAR2.IN VARCHAR2, tablename IN VARCHAR2, updatecolumn IN VARCHAR2 Next procedure is updatetables It is the loop control procedure for the trigger and calls updatecolumn PROCEDURE updatetables sourcetable IN VARCHAR2, oldvalue IN VARCHAR2.IN VARCHAR2 End of PACKAGE HEADER END cascadeupdate Now build package body That actually holds the.CREATE OR REPLACE PACKAGE BODY cascadeupdate AS PROCEDURE updatecolumn oldvalue IN VARCHAR2.IN VARCHAR2, tablename IN VARCHAR2, updatecolumn IN VARCHAR2AS define state variables for dbmssql procedures cur INTEGER rowsprocessed INTEGER start processing dbmsoutput calls are for debugging commented out during normal runtime BEGIN DBMSOUTPUT.PUTLINETable name tablename.Column updatecolumn .DBMSSQL. OPENCURSOR populate the initialized location with the.DBMSOUTPUT. PUTLINE UPDATE tablename set updatecolumnchr3.WHERE updatecolumnchr3.AND 11 dbmssql.UPDATE tablename set updatecolumnchr3.WHERE updatecolumnchr3.AND 11,dbmssql. DBMSSQL.EXECUTEcur close dynamic cursor to prepare for next.DBMSSQL. CLOSECURSORcur END PROCEDURE END updatecolumn PROCEDURE updatetables sourcetable IN VARCHAR2, oldvalue IN VARCHAR2.IN VARCHAR2 as Create the cursor to read records from bbssiteidtables Use to prohibit missing a column CURSOR gettablename IS SELECT.FROM. bbsupdatetables WHERE maintablesourcetable Define rowtype variable to hold record from.Use rowtype to allow for future changes.ROWTYPE start processing BEGIN open and fetch values with cursor OPEN gettablename FETCH gettablename INTO updaterec now that cursor status is open and values in.LOOP using the notfound status we had to pre populate record EXIT WHEN gettablenameNOTFOUND Initiate call to the updatecolumn procedure updatecolumnoldvalue, newvalue.Now get next record from table FETCH gettablename INTO updaterec processing returns to loop statement END LOOP close cursor and exit CLOSE gettablename end of procedure END updatetables end of package body END cascadeupdate Figure 2 The package containing the procedures for.Use of the DBMSSQL package to.The UPDATETABLES procedure.The procedure uses a.If desired, the table from.Using this information and the new and.UPDATECOLUMN. procedure dynamically rebuilds the table update command to update.Once the source table and.Figure 3 shows an example of this trigger.One thing to notice.UPDATETABLES procedure as well as the old and new values for the.This allows the UPDATETABLES procedure to.This. allows multiple master tables to utilize a single source table.The calling trigger has to be of the form CREATE OR REPLACE TRIGGER cascadeupdatelt tabname AFTER UPDATE OF lt column ON lt tabname.REFERENCING NEW AS upd OLD AS prev FOR EACH ROW BEGIN cascadeupdate.END Note how the table name is passed to the procedure, this.Figure 3 Example trigger utilizing the cascade update.Utilizing the procedures and.DBA can enforce a cascade update.PLSQL Triggers. A trigger is like a stored procedure that Oracle Database invokes automatically whenever a specified event occurs.Note. The database can detect only system defined events.You cannot define your own events.Topics. Overview of Triggers.Like a stored procedure, a trigger is a named PLSQL unit that is stored in the database and can be invoked repeatedly.Unlike a stored procedure, you can enable and disable a trigger, but you cannot explicitly invoke it.While a trigger is enabled, the database automatically invokes itthat is, the trigger fireswhenever its triggering event occurs.While a trigger is disabled, it does not fire.You create a trigger with the CREATETRIGGER statement.You specify the triggering event in terms of triggering statements and the item on which they act.The trigger is said to be created on or defined on the item, which is either a table, a view, a schema, or the database.You also specify the timing point, which determines whether the trigger fires before or after the triggering statement runs and whether it fires for each row that the triggering statement affects.By default, a trigger is created in the enabled state.For more information about the CREATETRIGGER statement, see CREATE TRIGGER Statement.If the trigger is created on a table or view, then the triggering event is composed of DML statements, and the trigger is called a DML trigger.For more information, see DML Triggers.If the trigger is created on a schema or the database, then the triggering event is composed of either DDL or database operation statements, and the trigger is called a system trigger.For more information, see System Triggers.A conditional trigger has a WHEN clause that specifies a SQL condition that the database evaluates for each row that the triggering statement affects.For more information about the WHEN clause, see WHEN condition.When a trigger fires, tables that the trigger references might be undergoing changes made by SQL statements in other users transactions.SQL statements running in triggers follow the same rules that standalone SQL statements do.Specifically Queries in the trigger see the current read consistent materialized view of referenced tables and any data changed in the same transaction.Updates in the trigger wait for existing data locks to be released before proceeding. Cara Update Software Sony Ericsson Live With Walkman Sony . An INSTEADOFtrigger is either A DML trigger created on either a noneditioning view or a nested table column of a noneditioning view.A system trigger defined on a CREATE statement.The database fires the INSTEADOF trigger instead of running the triggering statement.Note. A trigger is often called by the name of its triggering statement for example, DELETEtrigger or LOGONtrigger, the name of the item on which it is defined for example, DATABASEtrigger or SCHEMAtrigger, or its timing point for example, BEFOREstatement trigger or AFTEReach row trigger.Reasons to Use Triggers.Triggers let you customize your database management system.For example, you can use triggers to Automatically generate virtual column values.Log events. Gather statistics on table access.Modify table data when DML statements are issued against views.Enforce referential integrity when child and parent tables are on different nodes of a distributed database.Publish information about database events, user events, and SQL statements to subscribing applications.Prevent DML operations on a table after regular business hours.Prevent invalid transactions.Enforce complex business or referential integrity rules that you cannot define with constraints see How Triggers and Constraints DifferCaution.Triggers are not reliable security mechanisms, because they are programmatic and easy to disable.For high assurance security, use Oracle Database Vault, described in Oracle Database Vault Administrators Guide.How Triggers and Constraints Differ.Both triggers and constraints can constrain data input, but they differ significantly.A trigger always applies to new data only.For example, a trigger can prevent a DML statement from inserting a NULL value into a database column, but the column might contain NULL values that were inserted into the column before the trigger was defined or while the trigger was disabled.A constraint can apply either to new data only like a trigger or to both new and existing data.Constraint behavior depends on constraint state, as explained in Oracle Database SQL Language Reference.Constraints are easier to write and less error prone than triggers that enforce the same rules.However, triggers can enforce some complex business rules that constraints cannot.Oracle strongly recommends that you use triggers to constrain data input only in these situations To enforce referential integrity when child and parent tables are on different nodes of a distributed database.To enforce complex business or referential integrity rules that you cannot define with constraints.DML Triggers. A DML trigger is created on either a table or view, and its triggering event is composed of the DML statements DELETE, INSERT, and UPDATE.To create a trigger that fires in response to a MERGE statement, create triggers on the INSERT and UPDATE statements to which the MERGE operation decomposes.A DML trigger is either simple or compound.A simple DML trigger fires at exactly one of these timing points Before the triggering statement runsThe trigger is called a BEFOREstatement trigger or statement level.BEFOREtrigger. After the triggering statement runsThe trigger is called an AFTERstatement trigger or statement level.AFTERtrigger. Before each row that the triggering statement affectsThe trigger is called a BEFOREeach row trigger or row level.BEFOREtrigger. After each row that the triggering statement affectsThe trigger is called an AFTEReach row trigger or row level.AFTERtrigger. A compound DML trigger created on a table or editioning view can fire at one, some, or all of the preceding timing points.Compound DML triggers help program an approach where you want the actions that you implement for the various timing points to share common data.For more information, see Compound DML Triggers.A simple or compound DML trigger that fires at row level can access the data in the row that it is processing.For details, see Correlation Names and Pseudorecords.An INSTEADOFDMLtrigger is a DML trigger created on either a noneditioning view or a nested table column of a noneditioning view.For more information, see INSTEAD OF DML Triggers.A crossedition trigger is a simple or compound DML trigger for use only in edition based redefinition.For information about crossedition triggers, see Oracle Database Advanced Application Developers Guide.Except in an INSTEADOF trigger, a triggering UPDATE statement can include a column list.With a column list, the trigger fires only when a specified column is updated.Without a column list, the trigger fires when any column of the associated table is updated.For more information about the column list, see dmleventclause.Topics. Conditional Predicates for Detecting Triggering DML Statement.The triggering event of a DML trigger can be composed of multiple triggering statements.When one of them fires the trigger, the trigger can determine which one by using these conditional predicates Conditional Predicate.TRUE if and only if INSERTINGAn INSERT statement fired the trigger.UPDATINGAn UPDATE statement fired the trigger.UPDATING columnAn UPDATE statement that affected the specified column fired the trigger.DELETINGA DELETE statement fired the trigger.A conditional predicate can appear wherever a BOOLEAN expression can appear.Example 9 1 creates a DML trigger that uses conditional predicates to determine which of its four possible triggering statements fired it.Example 9 1 Trigger Uses Conditional Predicates to Detect Triggering Statement.CREATE OR REPLACE TRIGGER t.INSERT ORUPDATE OF salary, departmentid ORDELETE.WHEN INSERTING THEN.DBMSOUTPUT. PUTLINEInserting.WHEN UPDATINGsalary THEN.DBMSOUTPUT. PUTLINEUpdating salary.WHEN UPDATINGdepartmentid THEN.DBMSOUTPUT. PUTLINEUpdating department ID.WHEN DELETING THEN.DBMSOUTPUT. PUTLINEDeleting.Correlation Names and Pseudorecords.Note. This topic applies only to triggers that fire at row levelthat is, row level simple DML triggers and compound DML triggers with row level timing point sections.
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