How to avoid mutating error when insert or update record

Question

Hi ,
I have one transaction table which is having some detail record under one transaction number, after the one transaction number is over by insert or update, i
want to check the total amounts of one flag should be matched on same table if it is not then give error message. But i am getting mutating error on insert or update event trigger on statement level trigger on above table.
Is there any other way to avoid mutating error to solve the above problem or some temp table concepts to be used. help me its urgent.
Thanks in advance,
Sachin Khaladkar
Pune

Answer 1

Sachin, here's as short of an example as I could come up with on the fly. The sample data is ficticious and for example only.
Let's say I need to keep a table of items by category and my business rule states that the items in the table within each category must total to 100% at all times. So I want to insert rows and then make sure any category added sums to 100% or I will rollback the transation. I can't sum the rows in a row-level trigger because I'd have to query the table and it is mutating (in the middle of being changed by a transaction). Even if I could query it while it is mutating, there may be multiple rows in a category with not all yet inserted, so checking the sum after each row is not useful.
So here I will create;
1. the item table
2. a package to hold my record collection (associative array) for the trigger code (the category is used as a key to the array; if I insert 3 rows for a given category, I only need to sum that category once, right?
3. a before statement trigger to initialize the record collection (since package variables hang around for the entire database session, I need to clear the array before the start of every DML (INSERT in this case) statement against the item table)
4. a before row trigger to collect categories being inserted
5. an after statement trigger to validate my business rule
I then insert some sample data so you can see how it works. Let me know if you have any questions about this.
SQL> CREATE TABLE item_t
  2   (category  NUMBER(2)   NOT NULL
  3   ,item_code VARCHAR2(2) NOT NULL
  4   ,pct       NUMBER(3,2) NOT NULL);
Table created.
SQL>
SQL> CREATE OR REPLACE PACKAGE trg_pkg IS
  2    TYPE t_item_typ IS TABLE OF item_t.category%TYPE
  3      INDEX BY PLS_INTEGER;
  4    t_item       t_item_typ;
  5    t_empty_item t_item_typ;
  6  END trg_pkg;
  7  /
Package created.
SQL> SHOW ERRORS;
No errors.
SQL>
SQL> CREATE OR REPLACE TRIGGER item_bs_trg
  2    BEFORE INSERT
  3    ON item_t
  4  BEGIN
  5    DBMS_OUTPUT.put_line('Initializing...');
  6    trg_pkg.t_item := trg_pkg.t_empty_item;
  7  END item_bs_trg;
  8  /
Trigger created.
SQL> SHOW ERRORS;
No errors.
SQL>
SQL> CREATE OR REPLACE TRIGGER item_br_trg
  2    BEFORE INSERT
  3    ON item_t
  4    FOR EACH ROW
  5  BEGIN
  6    trg_pkg.t_item(:NEW.category) := :NEW.category;
  7    DBMS_OUTPUT.put_line('Inserted Item for Category: '||:NEW.category);
  8  END item_br_trg;
  9  /
Trigger created.
SQL> SHOW ERRORS;
No errors.
SQL>
SQL> CREATE OR REPLACE TRIGGER item_as_trg
  2    AFTER INSERT
  3    ON item_t
  4  DECLARE
  5    CURSOR c_item (cp_category item_t.category%TYPE) IS
  6      SELECT SUM(pct) pct
  7        FROM item_t
  8       WHERE category = cp_category;
  9  BEGIN
10    DBMS_OUTPUT.put_line('Verifying...');
11    FOR i IN trg_pkg.t_item.FIRST..trg_pkg.t_item.LAST LOOP
12      DBMS_OUTPUT.put_line('Checking Category: '||trg_pkg.t_item(i));
13      FOR rec IN c_item(trg_pkg.t_item(i)) LOOP
14        IF rec.pct != 1 THEN
15          RAISE_APPLICATION_ERROR(-20001,'Category '||trg_pkg.t_item(i)||' total = '||rec.pct);
16        END IF;
17      END LOOP;
18    END LOOP;
19  END item_as_trg;
20  /
Trigger created.
SQL> SHOW ERRORS;
No errors.
SQL> INSERT INTO item_t
  2    SELECT 1, 'AA', .3 FROM DUAL
  3    UNION ALL
  4    SELECT 2, 'AB', .6 FROM DUAL
  5    UNION ALL
  6    SELECT 1, 'AC', .2 FROM DUAL
  7    UNION ALL
  8    SELECT 3, 'AA',  1 FROM DUAL
  9    UNION ALL
10    SELECT 1, 'AA', .5 FROM DUAL
11    UNION ALL
12    SELECT 2, 'AB', .4 FROM DUAL;
Initializing...
Inserted Item for Category: 1
Inserted Item for Category: 2
Inserted Item for Category: 1
Inserted Item for Category: 3
Inserted Item for Category: 1
Inserted Item for Category: 2
Verifying...
Checking Category: 1
Checking Category: 2
Checking Category: 3
6 rows created.
SQL>
SQL> SELECT * FROM item_t ORDER BY category, item_code, pct;
  CATEGORY IT        PCT
         1 AA         .3
         1 AA         .5
         1 AC         .2
         2 AB         .4
         2 AB         .6
         3 AA          1
6 rows selected.
SQL>
SQL> INSERT INTO item_t
  2    SELECT 4, 'AB', .5 FROM DUAL
  3    UNION ALL
  4    SELECT 5, 'AC', .2 FROM DUAL
  5    UNION ALL
  6    SELECT 5, 'AA', .5 FROM DUAL
  7    UNION ALL
  8    SELECT 4, 'AB', .5 FROM DUAL
  9    UNION ALL
10    SELECT 4, 'AC', .4 FROM DUAL;
Initializing...
Inserted Item for Category: 4
Inserted Item for Category: 5
Inserted Item for Category: 5
Inserted Item for Category: 4
Inserted Item for Category: 4
Verifying...
Checking Category: 4
INSERT INTO item_t
ERROR at line 1:
ORA-20001: Category 4 total = 1.4
ORA-06512: at "PNOSKO.ITEM_AS_TRG", line 12
ORA-04088: error during execution of trigger 'PNOSKO.ITEM_AS_TRG'
SQL>
SQL> SELECT * FROM item_t ORDER BY category, item_code, pct;
  CATEGORY IT        PCT
         1 AA         .3
         1 AA         .5
         1 AC         .2
         2 AB         .4
         2 AB         .6
         3 AA          1
6 rows selected.
SQL>