Why don't databases use hash tables?

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With mysql For example

mysql It uses B+tree, Its advantage lies in 1. Range lookup 2. Less io Represents more search efficiency ：

1. hash Although the watch is O(1) The query efficiency of , But a lot of data will have a lot of hash Conflict , Query efficiency will also increase from O（1） Degenerate to O（n）.（ Although even tens of millions of data hash Tables are still more efficient than B+tree）
2. hash Table has no range lookup method , Can only traverse the whole table .

Please correct me if there is any mistake