多选题Which two statements are true regarding B-tree index（）AThe leaf blocks in the index are doubly linked.BThe leaf node stores a bitmap for each key value.CThe rows with NULL value in key columns also have entries in the index.DThe deletion of a row from
题目
多选题
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.