“…Timing and indexed data columns are the important factors affecting the index's reasonableness. Height of almost all the B-tree indexes is 2 or 3, so to find a key in the index usually takes only two or three times I /O [1]. The one kind of index scan mode which has pertinence includes index uniqueness scan, index range scan, index full scan and index fast full scan [2], so you can choose different indexes timing depending on the various situations [3].…”