MySQL 使用的是 BTree 还是 B+Tree

查看索引

查看表account的索引。

show index from account;

输出：

mysql> show index from account;
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table   | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| account |          0 | PRIMARY  |            1 | id          | A         |           3 |     NULL | NULL   |      | BTREE      |         |               |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

为什么是 BTREE

Index_type上显示的虽然是BTREE，但MySQL底层确实是用的B+Tree，外国友人猜测的可能原因：

1. B+TREE不是一个很好的关键词，+号是一个操作符。
2. 语法比InnoDB还早，可能比ISAM还早。

注意

B+Tree也是一种BTree啊！

参考

https://dba.stackexchange.com/questions/204561/does-mysql-use-b-tree-btree-or-both/204573

https://blog.jcole.us/2013/01/10/btree-index-structures-in-innodb