Which two statements are true regarding B-tree index? (Choose two.)
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.
A. index leaf blocks are doubly linked list.
Leaf blocks in both directions are inter-related, which facilitates key values in ascending or descending index scan. You can create secondary indexes on an index-organized tables to provide multiple access paths. Secondary indexes on index-organized tables differ from indexes on ordinary tables in two ways.
B. leaf nodes for each key-value store is a bitmap. WRONG. Is ROWID. Each index entry consists of the indexed columns (the key, column 2) and refers to the corresponding table row (via ROWID or RID).
C. Row index key column NULL value also has entries. WRONG. When all keys contained in a row as NULL, the bank has no corresponding index entries. Therefore, when the WHERE clause specifies NULL, it will always lead to a full table scan.
D. To delete a row will only lead to the index entry LOGICALLY DELETED. Delete all entries before the block, the space occupied by the deleted rows is not available for new entries. After deleting, it can be used for new entries.