变异 table - 触发错误

Question

我必须实现以下触发器：

The total number of votes, per election year, of the elections after 1960, does not exceed 538

但是，我得到了变异 table 错误。我明白为什么会出现错误，但我看不到其他解决方案（带触发器）。我可以创建一个临时的 table 但我只想拥有触发器。这是代码：

 CREATE OR REPLACE TRIGGER restrict_election_votes
 after INSERT OR UPDATE ON election
 for each row
 declare 
v_nbofvotes number;
v_eleyr election.election_year%type :=:NEW.election_year;
v_votes election.votes%type :=:NEW.VOTES;

begin 
select sum(votes)
into v_nbofvotes
from election
where election_year=v_eleyr;

if(v_votes+v_nbofvotes >538) 
THEN
    RAISE_APPLICATION_ERROR(-20500, 'Too many votes');
  END IF;

END;


update election
set votes=175
where candidate='MCCAIN J'
and election_year=2008;

Answer 1

你确定那里需要触发器吗？你可以用check constraint解决这个问题：

alter table election add consntraint too_many_votes check (votes < 538 or year < 1960);

Answer 2

假设问题是您需要查询选举table，因为总票数是根据多行确定的，那么如果您删除"for each row"并将其设为语句级触发器（将不得不更改查询以检查自 1960 年以来所有选举的 sum(votes) 规则，因为您不知道哪一行 inserted/updated）然后它将起作用。

create table mb_elct (year varchar2(4), cand varchar2(30), vt number)

create or replace trigger mb_elct_trg
after insert or update on mb_elct
declare 
   v_nbofvotes number;
begin
select count(*) 
into  v_nbofvotes
from (
  select year, sum(vt)
    from mb_elct
  where  year > '1960'
  group by year
  having sum(vt) >538
);

if(nvl(v_nbofvotes,0) != 0 ) 
THEN
    RAISE_APPLICATION_ERROR(-20500, 'Too many votes');
  END IF;

END;
/

insert into mb_elct values ('2008', 'McCain', 500);

1 row inserted

update mb_elct set vt = vt + 200 where year = '2008' and cand = 'McCain';
ORA-20500: Too many votes
ORA-06512: at "EDR_ADMIN.MB_ELCT_TRG", line 16
ORA-04088: error during execution of trigger 'EDR_ADMIN.MB_ELCT_TRG'

变异 table - 触发错误

Mutating table - trigger error

sql

oracle

triggers

plsql

mutating-table