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这篇文章主要讲解了“数据库触发器举例分析”,文中的讲解内容简单清晰,易于学习与理解,下面请大家跟着丸趣 TV 小编的思路慢慢深入,一起来研究和学习“数据库触发器举例分析”吧!
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;
/
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;
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;
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;
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。
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