请帮助,我试图允许/禁止插入名为'vol'的表,该表具有来自另一个表'avion'的外键(id_av)
create or replace trigger t
before insert on vol
declare etat VARCHAR(10);
BEGIN
select avion.etat into etat
from vol,etat
where avion.id_av = vol.id_av;
IF(etat <> 'disponible')
THEN
RAISE_APPLICATION_ERROR( -20001, 'insertion imposible');
END IF;
END t;
/
结果:触发器已创建,但当我尝试插入vol时,它显示了这些错误我也尝试过JOIN..ON,但没有真正解决
也许是这样的?
create or replace trigger t
before insert on vol
for each row --> edited
declare
etat VARCHAR(10);
BEGIN
-- MAX will prevent NO-DATA-FOUND
-- Also, you don't need join - use :NEW.ID_AV which is equal to currently inserted value
select max(avion.etat)
into etat
from avion
where avion.id_av = :new.id_av;
-- NVL because - if SELECT returns, nothing, you can't compare NULL with 'disponible'
IF nvl(etat, 'x') <> 'disponible'
THEN
RAISE_APPLICATION_ERROR( -20001, 'insertion imposible');
END IF;
END t;
/