OCP认证051考试题库：11g-v9.02-第170题

OCP认证051考试题库：11g-v9.02-第170题，完整题库请点击这里联系老师咨询了解

170. Which two statements are true regarding the DELETE and TRUNCATE commands? (Choose two.)

A. DELETE can be used to remove only rows from only one table at a time.

B. DELETE can be used to remove only rows from multiple tables at a time.

C. DELETE can be used only on a table that is a parent of a referential integrity constraint. 

D. DELETE can be used to remove data from specific columns as well as complete rows. 

E. DELETE and TRUNCATE can be used on a table that is a parent of a referential integrity constraint having ON DELETE rule .

Answer: AE

试题解析：

A，DELETE一次只能用于移除一个表的行，正确

B，DELETE一次只能用于移除多个表的行，错误，一次只能一个表

C，DELETE只能用于删除有引用完整性约束的父表，错误，有完整性约束的父表不能被删除，除非禁用约束等

D，DELETE可以用于删除指定列的数据以及完整的行，错误，只能删除行，不能删除列

E，DELETE和TRUNCATE可以用于有引用完整性约束ON DELETE规则的父表。正确。

建表时可以使用ON DELETE CASCADE(当删除父表数据时，子表数据也一起删除)或ON DELETE CASCAD SET NULL(当删除父表数据时，子表相关的列设置为NULL)子句，可以在SQL Language Reference里的Constraints部分查找到ON DELETE子句