小议Oracle外键约束修转业为（六）-PLSQL[Oracle防范]

SQL> DROP TABLE T_C;

表已删除.

SQL> DROP TABLE T_P;

表已删除.

SQL> CREATE TABLE T_P (ID NUMBER, NAME VARCHAR2(30));

表已成立.

SQL> ALTER TABLE T_P ADD PRIMARY KEY (ID);

表已更改.

SQL> CREATE TABLE T_C (ID NUMBER, FID NUMBER, NAME VARCHAR2(30));

表已成立.

SQL> ALTER TABLE T_C ADD CONSTRAINT FK_T_C
2 FOREIGN KEY (FID)
3 REFERENCES T_P (ID);

表已更改.

SQL> INSERT INTO T_P VALUES (1, 'A');

已成立 1 行.

SQL> INSERT INTO T_P VALUES (2, 'B');

已成立 1 行.

SQL> INSERT INTO T_C VALUES (1, 1, 'A');

已成立 1 行.

SQL> COMMIT;

提交完成.

查抄一下直接更新操作:

SQL> SELECT * FROM T_P;

ID NAME
---------- ------------------------------
1 A
2 B

SQL> SELECT * FROM T_C;

ID FID NAME
---------- ---------- ------------------------------
1 1 A

SQL> UPDATE T_P SET ID = 3 WHERE ID = 1;
UPDATE T_P SET ID = 3 WHERE ID = 1
*第 1 行呈现错误:
ORA-02292: 违反完好约束条件 (YANGTK.FK_T_C) - 已找到子记录日记

下面构造一个触发器:

SQL> CREATE OR REPLACE TRIGGER T_P_SET_DEFAULT
2 BEFORE DELETE OR UPDATE OF ID ON T_P
3 FOR EACH ROW
4 WHEN (NVL(NEW.ID, -1) != NVL(OLD.ID, -1))
5 DECLARE
6 V_STR VARCHAR2(32767);
7 BEGIN
8 FOR I IN (SELECT OWNER, TABLE_NAME, CONSTRAINT_NAME
9 FROM ALL_CONSTRAINTS
10 WHERE CONSTRAINT_TYPE = 'R'
11 AND R_OWNER = 'YANGTK'
12 AND R_CONSTRAINT_NAME IN
13 (SELECT CONSTRAINT_NAME FROM USER_CONSTRAINTS WHERE TABLE_NAME = 'T_P'))
14 LOOP
15 V_STR := 'UPDATE ' || I.TABLE_NAME || ' SET ';
16 FOR J IN (SELECT A.COLUMN_NAME, B.DATA_DEFAULT
17 FROM ALL_CONS_COLUMNS A, ALL_TAB_COLUMNS B
18 WHERE A.OWNER = I.OWNER
19 AND B.OWNER = I.OWNER
20 AND A.TABLE_NAME = I.TABLE_NAME
21 AND B.TABLE_NAME = I.TABLE_NAME
22 AND A.COLUMN_NAME = B.COLUMN_NAME
23 AND CONSTRAINT_NAME = I.CONSTRAINT_NAME)
24 LOOP
25 V_STR := V_STR || J.COLUMN_NAME || ' = ' || J.DATA_DEFAULT
26 || ' WHERE ' || J.COLUMN_NAME || ' = ' || :OLD.ID;
27 END LOOP;
28 EXECUTE IMMEDIATE V_STR;
29 END LOOP;
30 END;
31 /

触发器已成立

SQL> ALTER TABLE T_C MODIFY FID DEFAULT 2;

表已更改.

SQL> SELECT * FROM T_P;

ID NAME
---------- ------------------------------
1 A
2 B

SQL> SELECT * FROM T_C;

ID FID NAME
---------- ---------- ------------------------------
1 1 A

SQL> UPDATE T_P SET ID = 3 WHERE ID = 1;

已更新 1 行.

SQL> SELECT * FROM T_P;

ID NAME
---------- ------------------------------
3 A
2 B

SQL> SELECT * FROM T_C;

ID FID NAME
---------- ---------- ------------------------------
1 2 A

下面查抄一下DELETE操作能否有效:

SQL> UPDATE T_C SET FID = 3;

已更新 1 行.

SQL> SELECT * FROM T_C;

ID FID NAME
---------- ---------- -----------------------------
1 3 A

SQL> DELETE T_P WHERE ID = 3;

已删除 1 行.

SQL> SELECT * FROM T_P;

ID NAME
---------- ------------------------------
2 B

SQL> SELECT * FROM T_C;

ID FID NAME
---------- ---------- -----------------------------
1 2 A