多选题Which two statements are true about a bitmap index？ （）AIt is recommended for the columns that have unique values.BIt can be converted to a B-tree index by using the ALTER INDEX command.CIt has a bitmap segment for each distinct value in the key column，

第1题：

While designing your database， you have created the EMPLOYEES table as an index-organized table （IOT）. You want to create a bitmap index on the JOB_ID column to make queries faster. Which task must have been completed so that you are able to create the bitmap index？（） 

• A、A primary key must have been created.
• B、A mapping table must have been created.
• C、An overflow tablespace must have been specified.
• D、The PCTTHRESHOLD option must have been specified.

第2题：

Which two statements are true about constraints? （）

• A、The UNIQUE constraint does not permit a null value for the column.
• B、A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
• C、The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.
• D、The NOT NULL constraint ensures that null values are not permitted for the column.

第3题：

Which two statements are true about a bitmap index？ （）

• A、It is recommended for the columns that have unique values.
• B、It can be converted to a B-tree index by using the ALTER INDEX command.
• C、It has a bitmap segment for each distinct value in the key column， containing a string of bits in which each bit represents the presence or absence of a key column value.
• D、Updating the key column locks the whole bitmap segment that contains the bit for the key value to be updated.

第4题：

Which two statements are true regarding B-tree index（）

• A、The leaf blocks in the index are doubly linked.
• B、The leaf node stores a bitmap for each key value.
• C、The rows with NULL value in key columns also have entries in the index.
• D、The deletion of a row from the table causes a logical deletion in index leaf block and the space becomes available for the new leaf entry.

第5题：

A bitmap join index is defined as（）.

• A、An index used to join two bitmap indexes on a table.
• B、A bitmap index created for the join of two or more tables.
• C、A bitmap index created on the join of two or more indexes.
• D、A bitmap index created on the join of two or more indexed-organized tables.

第6题：

The InnoDB engine has a feature known as clustered indexes. Which three statements are true about clustered indexes as used in InnoDB?（）

• A、A primary key must exist for creation of a clustered index
• B、A clustered index allows fulltext searching within InnoDB
• C、The first unique index is always used as a clustered index and not a primary key
• D、A clustered index provides direct access to a page containing row data
• E、If no indexes exist, a hidden clustered index is generated based on row IDs
• F、A primary key is used as a clustered index
• G、A clustered index is a grouping of indexes from different tables into a global index for faster searching

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第13题：

Which two statements are true about the primary key constraint in a table？ （）

• A、It is not possible to disable the primary key constraint.
• B、It is possible to have more than one primary key constraint in a single table.
• C、The primary key constraint can be referred by only one foreign key constraint.
• D、The primary key constraint can be imposed by combining more than one column.
• E、The non-deferrable primary key constraint creates an unique index on the primary key column if it is not already indexed.

第14题：

Which two statements are true regarding B-tree indexs（）

• A、The leaf blocks in the index are doubly linked.
• B、The leaf node stores a bitmap for each key value.
• C、The rows with NULL value in key columns also have entries in the index.
• D、The deletion of a row from the table causes a logical deletion in index leaf block and the space becomesavailable for the new leaf entry

第15题：

You are using Oracle Enterprise Manager to estimate the size of a table to be created. You have typed data regarding the column names， data types， sizes of the columns， and the projected number of rows in the table. Which additional information does the Oracle Enterprise Manager return？（）

• A、 space allocated in the tablespace
• B、 space required for the bitmap index on a column of the table
• C、 space remaining in the tablespace after creating the table
• D、 estimated value of the PCTFREE storage parameter

第16题：

Why does performance degrade when many UPDATE， INSERT， or DELETE statements are issued on a tablethat has an associated Bitmap index（）

• A、The DML operations re-create the Bitmap index blocks.
• B、The Bitmap index is rebuilt automatically after a DML operation.
• C、The smallest amount of a bitmap that can be locked is a bitmap segment.
• D、Additional time is taken to remove NULL values from the Bitmap index after a DML operation.

第17题：

You have altered a non-unique index to be invisible to determine if queries execute within an acceptable response time without using this index. Which two are possible if table updates are performed which affect the invisible index columns?（）

• A、The index remains invisible.
• B、The index is not updated by the DML statements on the indexed table.
• C、The index automatically becomes visible in order to have it updated by DML on the table.
• D、The index becomes unusable but the table is updated by the DML.
• E、The index is updated by the DML on the table.

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