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我们维护一张客户表，这张表的内容在周六和周日不允许修改。这就是客户表：
CREATE TABLE plch_customers ( custnum INTEGER , custname VARCHAR2 (100) )
我需要创建一个触发器来阻止周末对这张表的任何插入、修改和删除。我写了这些代码：
CREATE OR REPLACE TRIGGER plch_customers_maint_trg
/*TEXT*/
DECLARE
BEGIN
IF TO_CHAR (SYSDATE, 'DY', 'NLS_DATE_LANGUAGE=ENGLISH')
IN ('SAT', 'SUN')
THEN
RAISE_APPLICATION_ERROR (-20000
, 'Customers maintained Monday-Friday only.');
END IF;
END;
/
哪些选项可用来取代文中的/*TEXT*/, 使得这个触发器不允许周末对plch_customers表执行任何DML操作，并且每个语句只触发一次？
(A)
BEFORE UPDATE ON plch_customers FOR EACH ROW BEFORE INSERT ON plch_customers FOR EACH ROW BEFORE DELETE ON plch_customers FOR EACH ROW
SQL>
CREATE OR REPLACE TRIGGER plch_customers_maint_trg
BEFORE UPDATE ON plch_customers FOR EACH ROW
BEFORE INSERT ON plch_customers FOR EACH ROW
BEFORE DELETE ON plch_customers FOR EACH ROW
DECLARE
BEGIN
IF TO_CHAR (SYSDATE, 'DY', 'NLS_DATE_LANGUAGE=ENGLISH')
IN ('SAT', 'SUN')
THEN
RAISE_APPLICATION_ERROR (-20000
, 'Customers maintained Monday-Friday only.');
END IF;
END;
ORA-04079: 无效的触发器说明
SQL>
(B)
BEFORE UPDATE ON plch_customers BEFORE INSERT ON plch_customers BEFORE DELETE ON plch_customers
SQL>
CREATE OR REPLACE TRIGGER plch_customers_maint_trg
BEFORE UPDATE ON plch_customers
BEFORE INSERT ON plch_customers
BEFORE DELETE ON plch_customers
DECLARE
BEGIN
IF TO_CHAR (SYSDATE, 'DY', 'NLS_DATE_LANGUAGE=ENGLISH')
IN ('SAT', 'SUN')
THEN
RAISE_APPLICATION_ERROR (-20000
, 'Customers maintained Monday-Friday only.');
END IF;
END;
ORA-04079: 无效的触发器说明
SQL>
(C)
BEFORE UPDATE, INSERT OR DELETE ON plch_customers
SQL>
CREATE OR REPLACE TRIGGER plch_customers_maint_trg
BEFORE UPDATE, INSERT OR DELETE ON plch_customers
DECLARE
BEGIN
IF TO_CHAR (SYSDATE, 'DY', 'NLS_DATE_LANGUAGE=ENGLISH')
IN ('SAT', 'SUN')
THEN
RAISE_APPLICATION_ERROR (-20000
, 'Customers maintained Monday-Friday only.');
END IF;
END;
ORA-00969: 缺失 ON 关键字
SQL>
(D)
BEFORE UPDATE OR INSERT OR DELETE ON plch_customers FOR EACH ROW
SQL> Trigger created SQL>
(E)
BEFORE UPDATE OR INSERT OR DELETE ON plch_customers
SQL> Trigger created SQL>
答案E
D不是答案因为每行都会触发，不满足条件。
感谢各位的阅读，以上就是“数据库触发器举例分析”的内容了，经过本文的学习后，相信大家对数据库触发器举例分析这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是云搜网，小编将为大家推送更多相关知识点的文章，欢迎关注！
