How to avoid “table mutating” errors

Question

I have an trigger that needs to read from a table after deleting a row. Essentially, I need to count up the remaining rows that are similar to the current row, and if that c

Answer 1

You can create a COMPOUND trigger for such cases:

create or replace TRIGGER Di_PatMustBeWell
FOR DELETE ON Diagnosis
COMPOUND TRIGGER

    TYPE Di_Patient_Table_type IS TABLE OF DiagnosisCount.Di_Patient%TYPE;
    Di_Patient_Table Di_Patient_Table_type;

     BEFORE STATEMENT IS
      BEGIN
        Di_Patient_Table := Di_Patient_Table_type();
     END BEFORE STATEMENT;

     BEFORE EACH ROW IS
     BEGIN
        Di_Patient_Table.EXTEND;
        Di_Patient_Table(Di_Patient_Table.LAST) := :OLD.Di_Patient;
     END BEFORE EACH ROW;

    AFTER STATEMENT IS
    BEGIN
       FOR i IN Di_Patient_Table.FIRST..Di_Patient_Table.LAST LOOP
          SELECT NUMDISEASES INTO Numdiseases
          FROM DiagnosisCount
          where Di_Patient = Di_Patient_Table(i);

          IF NumDiseases !=  1 THEN
            UPDATE Patient SET Pat_Sick = 0 WHERE Pat_Person = Di_Patient_Table(i);
          END IF;
       END LOOP;
       Di_Patient_Table.DELETE;
     END AFTER STATEMENT;
   END;
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