Oracle Table Mutating Error
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Mutating Trigger With Example
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Oracle Mutating Trigger Pragma Autonomous Transaction
7 down vote favorite 1 I understand mutating table errors are caused by a design flaw or problematic query. An old query was recently put into production which throws a mutating table error. Our DBA solved the problem but we do not know how. What exactly causes mutating table errors and how would our DBA have fixed the problem? sql oracle trigger plsql share|improve this question edited Jun 25 '15 at 17:56 Mahi_0707 1033 asked Sep 6 '11 at 8:46 parmanand 112238 add oracle statement level trigger a comment| 3 Answers 3 active oldest votes up vote 13 down vote accepted The most likely cause of a mutating table error is the misuse of triggers. Here is a typical example: you insert a row in table A a trigger on table A (for each row) executes a query on table A, for example to compute a summary column Oracle throws an ORA-04091: table A is mutating, trigger/function may not see it This is an expected and normal behaviour, Oracle wants to protect you from yourself since Oracle guarantees: (i) that each statement is atomic (i.e will either fail or succeed completely) (ii) that each statement sees a consistent view of the data Most likely when you write this kind of trigger you would expect the query (2) to see the row inserted on (1). This would be in contradiction with both points above since the update is not finished yet (there could be more rows to be inserted). Oracle could return the result consistent with a point in time just before the beginning of the statement but from most of the examples I have seen that try to implement this logic, people see a multi-row statement as a serie of successive steps and expect the statement [2] to see the changes made by the previous steps. Oracle can not return the expected result and therefore throws the error. For further reading: "mutating table" on Ask Tom. If as I suspect the cause of the mutating
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Ora-04091 Solution
Fix Oracle mutating trigger oracle instead of trigger table errors Oracle Database Tips by Burleson Consulting A mutation table is defined as a table that is changing. But mutating table error in oracle 11g with example in dealing with triggers, it is a table 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 http://dba.stackexchange.com/questions/5432/what-are-the-causes-and-solutions-for-mutating-table-errors table that it read from. This does not impact the 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 http://www.dba-oracle.com/t_avoiding_mutating_table_error.htm the Oracle database reduces the impact of the mutating table error on triggers and they are 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 t
Social Links Printer Friendly About Search 8i | 9i | 10g | 11g | 12c | 13c | Misc | PL/SQL | SQL | RAC | WebLogic | Linux https://oracle-base.com/articles/9i/mutating-table-exceptions Home » Articles » 9i » Here Mutating Table Exceptions Mutating table exceptions http://stackoverflow.com/questions/16182089/table-is-mutating-trigger-function-may-not-see-it-stopping-an-average-grade-fr occur when we try to reference the triggering 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 mutating trigger (Global Temporary Table) Test Schema The following schema objects are necessary to run the 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 ); mutating trigger in 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 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 ERRO
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Table is mutating, trigger/function may not see it (stopping an average grade from dropping below 2.5) up vote 1 down vote favorite Here's the problem: Create a trigger that prevents any change to the taking relation that would drop the overall average grade in any particular class below 2.5. Note: This trigger is not intended to address the average GPA of any given student, but rather it should address the average grade for all grades assigned in a particular class. Here's the schema: Student-schema =(studentnum, name, standing, gpa, major) Class-schema = (schedulenum, semester, department, classnum, days, time, place, enrollment) Instructor-schema = (name, department, office) Teaches-schema = (name, schedulenum, semester) Taking-schema = (studentnum, schedulenum, semester, grade) I'm having a terrible time with these triggers, but here's my attempt to make this work: CREATE OR REPLACE TRIGGER stopChange AFTER UPDATE OR INSERT OR DELETE ON taking REFERENCING OLD AS old NEW AS new FOR EACH ROW DECLARE grd_avg taking.grade%TYPE; BEGIN SELECT AVG(grade) INTO grd_avg FROM taking WHERE studentnum = :new.studentnum AND schedulenum = :new.schedulenum AND semester = :new.semester; IF grd_avg < 2.5 THEN UPDATE taking SET grade = :old.grade WHERE studentnum = :old.studentnum AND schedulenum = :old.schedulenum AND semester = :old.semester; END IF; END; / I'm obviously doing something wrong because when I then go to update or delete a tuple, I get the error: ERROR at line 1: ORA-0409