Question

我有一个问题，我正在尝试解决一个触发器，该触发器必须检查对象是否保存在表中。但是，如果我选择的元素与要插入的鳕鱼对象相同，则选择此对象表中不存在触发器将使我获得异常，但找不到数据。.如果触发器使我没有获得数据，我该怎么办？

我可以这样做吗？

EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO VALUES TABLE_X (:NEW.A,:NEW.B,:NEW.C)

Answer 1

是的，你可以做。

请考虑以下内容：

SQL> CREATE TABLE TABLE_X(A INT, B INT, C INT);

Table created
SQL> CREATE TABLE TABLE_Y(A INT, B INT, C INT);

Table created

SQL> CREATE OR REPLACE TRIGGER trg_bi_ins_y
  2  BEFORE INSERT ON TABLE_Y
  3  FOR EACH ROW
  4  DECLARE
  5    V_A TABLE_Y.A%TYPE;
  6  BEGIN
  7   BEGIN
  8       SELECT Y.A
  9         INTO V_A
 10         FROM TABLE_Y Y
 11        WHERE Y.A = :NEW.A;
 12     EXCEPTION
 13      WHEN NO_DATA_FOUND THEN
 14         INSERT INTO TABLE_X VALUES(:NEW.A,:NEW.B,:NEW.C);
 15   END;
 16  END;
 17  /

Trigger created

SQL> INSERT INTO TABLE_Y VALUES(1,0,0); 

1 row inserted

SQL> SELECT * FROM TABLE_Y;

 A   B   C
--- --- ---
 1   0   0

SQL> SELECT * FROM TABLE_X;

 A   B   C
--- --- ---
 1   0   0

-- the row with value 1 for column A does not exist, and insertion to TABLE_X occurs.

SQL> INSERT INTO TABLE_Y VALUES(1,1,1);

1 row inserted


SQL> SELECT * FROM TABLE_Y;

 A   B   C
--- --- ---
 1   0   0
 1   1   1

SQL> SELECT * FROM TABLE_X; 

 A   B   C
--- --- ---
 1   0   0

-- the row with value 1 for column A already exists, and no insertion occurs.

没有数据时出现PL / SQL异常

1 个答案: