多选题Which two statements are true regarding B-tree indexs（）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 the table causes a logical deletion in index leaf block and the space becomesavailable for the new leaf entry
多选题
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
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