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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：

CREATETABLEplch_customers(custnumINTEGER,custnameVARCHAR2(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：

CREATEORREPLACETRIGGERplch_customers_maint_trg/*TEXT*/DECLAREBEGINIFTO_CHAR(SYSDATE,'DY','NLS_DATE_LANGUAGE=ENGLISH')IN('SAT','SUN')THENRAISE_APPLICATION_ERROR(-20000,'CustomersmaintainedMonday-Fridayonly.');ENDIF;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)

BEFOREUPDATEONplch_customersFOREACHROWBEFOREINSERTONplch_customersFOREACHROWBEFOREDELETEONplch_customersFOREACHROW

SQL>CREATEORREPLACETRIGGERplch_customers_maint_trgBEFOREUPDATEONplch_customersFOREACHROWBEFOREINSERTONplch_customersFOREACHROWBEFOREDELETEONplch_customersFOREACHROWDECLAREBEGINIFTO_CHAR(SYSDATE,'DY','NLS_DATE_LANGUAGE=ENGLISH')IN('SAT','SUN')THENRAISE_APPLICATION_ERROR(-20000,'CustomersmaintainedMonday-Fridayonly.');ENDIF;END;ORA-04079:无效的触发器说明SQL>

(B)

BEFOREUPDATEONplch_customersBEFOREINSERTONplch_customersBEFOREDELETEONplch_customers

SQL>CREATEORREPLACETRIGGERplch_customers_maint_trgBEFOREUPDATEONplch_customersBEFOREINSERTONplch_customersBEFOREDELETEONplch_customersDECLAREBEGINIFTO_CHAR(SYSDATE,'DY','NLS_DATE_LANGUAGE=ENGLISH')IN('SAT','SUN')THENRAISE_APPLICATION_ERROR(-20000,'CustomersmaintainedMonday-Fridayonly.');ENDIF;END;ORA-04079:无效的触发器说明SQL>

(C)

BEFOREUPDATE,INSERTORDELETEONplch_customers

SQL>CREATEORREPLACETRIGGERplch_customers_maint_trgBEFOREUPDATE,INSERTORDELETEONplch_customersDECLAREBEGINIFTO_CHAR(SYSDATE,'DY','NLS_DATE_LANGUAGE=ENGLISH')IN('SAT','SUN')THENRAISE_APPLICATION_ERROR(-20000,'CustomersmaintainedMonday-Fridayonly.');ENDIF;END;ORA-00969:缺失ON关键字SQL>

(D)

BEFOREUPDATEORINSERTORDELETEONplch_customersFOREACHROW

SQL>TriggercreatedSQL>

(E)

BEFOREUPDATEORINSERTORDELETEONplch_customers

SQL>TriggercreatedSQL>

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。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！