choose three

Which three statements are true about indexes and their administration in an Orade database?

A) An INVISIBLE index is not maintained when Data Manipulation Language (DML) is performed on its underlying table.

B) An index can be created as part of a CREATE TABLE statement.

C) A DROP INDEX statement always prevents updates to the table during the drop opeaton

D) A UNIQUE and non-unique index can be ceated on the same table colunn

E) A descending index is a type of funcion-based index

F) If a query filters on an indexed column then it will always be used during execution of the query

Answer：BCE

(解析：建表的时候就可以创建索引;做 drop index 时会锁表;

创建降序排列的索引：

create index idx_emp_ename on emp(ename DESC) ;

创建了索引，在查询的时候不一定都会用到，涉及的因素很多。

)