Table Mutating Trigger

When a Trigger is created on a table and the trigger code is performing the read operation on the same table, then the mutating happens.

CREATE TRIGGER sample_trigger
 AFTER INSERT
    ON sample_table
   FOR EACH ROW
local_variable NUMBER;
BEGIN
  IF INSERTING
  THEN
    SELECT sample_column
      INTO local_variable
      FROM sample_table;
  .
  .
  .

  END IF;
END sample_trigger;

To resolve this, we need to store the required values in global variables when row level trigger is fired and create a statement level trigger which uses this global variable.

CREATE PACKAGE sample_package AS
  global_variable NUMBER;
END sample_package;

--row level trigger

CREATE TRIGGER sample_trigger_1
 AFTER INSERT
    ON sample_table
   FOR EACH ROW
BEGIN
  IF INSERTING
  THEN
    global_variable := :NEW.sample_column;
  END IF;
END sample_trigger_1;

--statement level trigger

CREATE TRIGGER sample_trigger_2
 AFTER INSERT
    ON sample_table
BEGIN
  IF INSERTING
  THEN
    local_variable := global_variable;
  .
  .
  .

  END IF;
END sample_trigger_2;

Disadvantage: It will be useful only when COMMIT happens for each and every row separately. It will not be useful when COMMIT happens after multiple updates. The second trigger fires only after COMMIT and the required operation happens only for the last row.