How To Avoid Mutating Table Error
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Burleson Consulting A mutation table is defined as a table that is changing. But in dealing with triggers, it is a table mutating trigger with example that has the possibility of changing. What this means to a trigger is that if the trigger reads a table, it can not change the table that it read from. This does not impact the oracle mutating trigger pragma autonomous transaction exclusive use of :OLD and :NEW. It says that if the trigger reads the table (such as using a SELECT query), that changes (even using :NEW) will fail. This can also happen when a trigger on a parent table causes an insert on a child table referencing a foreign key. Mutating Tables Each new release of the Oracle database reduces the impact of the mutating table error on triggers and they are
Oracle Statement Level Trigger
much less of a problem with Oracle9i and above. If a trigger does result in a mutating table error, the only real option is to rewrite the trigger as a statement-level trigger. Mutating table errors only impact row level triggers. But to use a statement level trigger, some data may need to be preserved from each row, to be used by the statement level trigger. This data can be stored in a PL/SQL collection or in a temporary table. A simple row level trigger that causes a mutating table error can result in a very complicated statement level trigger to achieve the needed result. Here are some important items to remember about triggers. On insert triggers have no :OLD values. On delete triggers have no :NEW values. Triggers do not commit transactions. If a transaction is rolled back, the data changed by the trigger is also rolled back. Commits, rollbacks and save points are not allowed in the trigger body. A commit/rollback affects the entire transaction, it is all or none. Unhandled exceptions in the trigger will cause a rollback of the entire transaction, not just the trigger. If more than one trigger is defined on an event, the order in which they fire is not defined. If the triggers must fire in ord
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Social Links Printer Friendly About Search 8i | 9i | 10g | 11g | 12c | 13c | Misc | PL/SQL | SQL | RAC | WebLogic | Linux Home » Articles » 9i » Here https://oracle-base.com/articles/9i/mutating-table-exceptions Mutating Table Exceptions Mutating table exceptions occur when we try to reference the triggering http://www.techrepublic.com/article/learn-to-avoid-the-mutating-table-problem-in-oracle/ table in a query from within row-level trigger code. In this article I'll present examples of how a mutating table exception might occur and simple methods to get round it. Test Schema Mutating Table Demonstration Solution 1 (Collection in Package Variable) Solution 2 (Global Temporary Table) Test Schema The following schema objects are necessary to run the mutating trigger code in this article. CREATE TABLE tab1 ( id NUMBER(10) NOT NULL, description VARCHAR2(50) NOT NULL ); ALTER TABLE tab1 ADD ( CONSTRAINT tab1_pk PRIMARY KEY (id) ); CREATE SEQUENCE tab1_seq; CREATE TABLE tab1_audit ( id NUMBER(10) NOT NULL, action VARCHAR2(10) NOT NULL, tab1_id NUMBER(10), record_count NUMBER(10), created_time TIMESTAMP ); ALTER TABLE tab1_audit ADD ( CONSTRAINT tab1_audit_pk PRIMARY KEY (id) ); ALTER TABLE tab1_audit ADD ( CONSTRAINT tab1_audit_tab1_fk FOREIGN KEY (tab1_id) REFERENCES mutating trigger in tab1(id) ); CREATE SEQUENCE tab1_audit_seq; Mutating Table Demonstration Let's assume we need to audit the actions on the parent table and for some reason, this involves querying the triggering table. We can demonstrate this with the following package and trigger. We place all our trigger code into a package as follows. CREATE OR REPLACE PACKAGE trigger_api AS PROCEDURE tab1_row_change (p_id IN tab1.id%TYPE, p_action IN VARCHAR2); END trigger_api; / SHOW ERRORS CREATE OR REPLACE PACKAGE BODY trigger_api AS PROCEDURE tab1_row_change (p_id IN tab1.id%TYPE, p_action IN VARCHAR2) IS l_count NUMBER(10) := 0; BEGIN SELECT COUNT(*) INTO l_count FROM tab1; INSERT INTO tab1_audit (id, action, tab1_id, record_count, created_time) VALUES (tab1_audit_seq.NEXTVAL, p_action, p_id, l_count, SYSTIMESTAMP); END tab1_row_change; END trigger_api; / SHOW ERRORS Next we create the row-level trigger itself to catch any changes to the table. CREATE OR REPLACE TRIGGER tab1_ariu_trg AFTER INSERT OR UPDATE ON tab1 FOR EACH ROW BEGIN IF inserting THEN trigger_api.tab1_row_change(p_id => :new.id, p_action => 'INSERT'); ELSE trigger_api.tab1_row_change(p_id => :new.id, p_action => 'UPDATE'); END IF; END; / SHOW ERRORS If we try to insert into the TAB1 table we might expect the insert to complete and the audit record to be created but as you can see below this is not the case. SQL> INSERT INTO tab1 (id, description) VALUES (tab1_seq.NEXTVAL, 'ON
United States Australia United Kingdom Japan Newsletters Forums Resource Library Tech Pro Free Trial Membership Membership My Profile People Subscriptions My stuff Preferences Send a message Log Out TechRepublic Search GO Topics: CXO Cloud Big Data Security Innovation Software Data Centers Networking Startups Tech & Work All Topics Sections: Photos Videos All Writers Newsletters Forums Resource Library Tech Pro Free Trial Editions: US United States Australia United Kingdom Japan Membership Membership My Profile People Subscriptions My stuff Preferences Send a message Log Out Data Management Learn to avoid the mutating table problem in Oracle Mutating tables in Oracle can drive any IT database manager insane when it comes to tracking down the culprit. With a clear idea of the table design required, however, this problem can be avoided. By Scott Robinson | April 14, 2003, 12:00 AM PST RSS Comments Facebook Linkedin Twitter More Email Print Reddit Delicious Digg Pinterest Stumbleupon Google Plus Tables are everything to IT database managers in ERP database environments. The organization of database tables, their relationships, and the manner in which they are managed are a fair indicator of the overall quality of performance you can expect from the system.So when something can happen to mess up your tables, you want to watch out for it. In Oracle, there’s a nasty snare out there waiting for you. It's Oracle error ORA-04091, the mutating table error, and the best way to deal with it is to avoid it altogether. This article will explain why.When tables mutateThere are several causes of mutating tables, but in general a table mutation error will result if you create a trigger on a table that attempts to examine the current table. Also, the error is given when an attempt is made to examine a parent table in a cascading update/delete.Why are these considered errors? It’s obvious when you think about it: The trigger is trying to change or examine something that’s already being changed. This confuses Oracle, and understandably so. In a row-level trigger firing, when the trigger is about to fire for the second row in a multirow update, what is Oracle to do? Does the application intend that Oracle s