触发器:如何初始化一个表的值和另一个表的值? [英] Triggers: how can I initialize the value on a table with a value on another?
问题描述
我正在创建一个触发器,以使用表MODELO上的capacidad值初始化表VUELO上的plazas_disponibles值.像这样:
I'm creating a trigger to initialize the value plazas_disponibles on table VUELO with the value capacidad on table MODELO. Like this:
create or replace
TRIGGER inicializar_plazas_disponibles
BEFORE INSERT OR UPDATE ON VUELO
BEGIN
SET VUELO (plazas_disponibles) = MODELO (capacidad);
END inicializar_plazas_disponibles;
我遇到以下错误:
Error(2,10): PL/SQL: SQL Statement ignored
Error(2,14): PL/SQL: ORA-00922: missing or invalid option
Error(2,23): PL/SQL: ORA-00971: missing SET keyword
为什么?
推荐答案
Because that isn't how you change a value in the row being inserted - you need to modify it using the :NEW
syntax (documentation); and you haven't shown how to retrieve a relevant value from the MODELO
table.
您需要执行以下操作:
CREATE OR REPLACE TRIGGER inicializar_plazas_disponibles
BEFORE INSERT OR UPDATE ON vuelo
FOR EACH ROW
BEGIN
SELECT capacidad
INTO :NEW.plazas_disponibles
FROM modelo
WHERE ... some condition, presumably another :NEW column ...
END;
(尽管我不确定是否可以直接选择一个 :NEW
值-请尝试尝试该方法,但是如果不能,则需要声明相同类型的变量,而是选择一个相同类型的变量,然后将其分配给:NEW
).
(Although I'm not entirely sure whether you can select straight into a :NEW
value - try that, but if not you'll need to declare a variable of the same type, select into that instead, and then assign that to the :NEW
).
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