如何避免 "table mutating" 错误

Question

我有一个触发器需要在删除行后从 table 中读取。本质上，我需要计算与当前行相似的剩余行，如果该计数为零，则更新别处的字段。

经过两天的反复思考，我一直无法弄清楚如何重组我的思维过程来让我做到这一点。这是一个例子：

CREATE OR REPLACE TRIGGER Di_PatMustBeWell
AFTER DELETE 
    ON Diagnosis
    FOR EACH ROW
Declare
    --PRAGMA AUTONOMOUS_TRANSACTION;
    NumDiseases Number;
BEGIN
    SELECT NUMDISEASES INTO Numdiseases
    FROM DiagnosisCount
    where Di_Patient = :OLD.Di_Patient;

    IF( NumDiseases !=  1 ) THEN
        UPDATE Patient SET Pat_Sick = 0 WHERE Pat_Person = :OLD.Di_Patient;
    END IF;
END;
/

Answer 1

简短回答 - 没有触发器，没有变异。

您可以使用带有 pragma autonomous_transaction 的触发器来计算特定患者的剩余诊断数，但不推荐这样做。最好创建新函数或过程来实现已删除诊断的逻辑。像这样：

create table Diagnosis as select 456 idDiseases, 123 di_patient from dual;
/
create table diagnosisCount as select 1 numDiseases, 123 di_patient from dual;
/
create table Patient as select 123 Pat_Person, 1 Pat_Sick from dual;
/
drop trigger di_patmustbewell;

create or replace function deleteDiagnosis(idDiseases number) return number is
    rows_ number;
    di_patient number;
    Numdiseases number;
begin
    <<del>> begin 
        delete Diagnosis where IdDiseases = deleteDiagnosis.IdDiseases
        returning Diagnosis.di_patient into deleteDiagnosis.di_patient
        ;
        rows_ := sql%rowcount;
        if rows_ != 1 then raise too_many_rows; end if;
    end del;
    select count(1) into deleteDiagnosis.numDiseases from Diagnosis where Di_Patient = deleteDiagnosis.di_patient;
    if deleteDiagnosis.numdiseases = 0 then <<upd>> begin 
        update Patient set Pat_Sick = 0 where Pat_Person = deleteDiagnosis.di_patient;
        exception when others then 
            dbms_output.put_line('Cannot update Patient di_patient='||di_patient);
            raise;
    end upd; end if;
    return rows_;
end;
/
show errors

declare rows_ number :=  deleteDiagnosis(456);
begin dbms_output.put_line('deleted '||rows_||' rows'); end;
/

deleted 1 rows

select * from Patient;
PAT_PERSON   PAT_SICK
---------- ----------
       123          0

另一种解决方案，如果您喜欢（或必须）在您的应用程序中使用触发器 - 在触发器主体中声明返回患者诊断计数的内部函数：

create or replace trigger di_patmustbewell
after delete on diagnosis for each row
declare
    numdiseases number;
    function getNumDiagnosis (di_patient number) return number is
        ret number;
        pragma autonomous_transaction;
    begin
        select count(1) into ret from diagnosis where di_patient = getNumDiagnosis.di_patient;
        return ret;
    end getNumDiagnosis;    
begin
    numDiseases := getNumDiagnosis(:old.di_patient);
    if(numdiseases = 0) then
        update patient set pat_sick = 0 where pat_person = :old.di_patient;
    end if;
end;
/
show errors;

Trigger DI_PATMUSTBEWELL compiled

希望对您有所帮助。

Answer 2

您可以为这种情况创建复合触发器：

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;
/

如何避免 "table mutating" 错误

How to avoid "table mutating" errors

sql

oracle

database-trigger