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git-zjx avatar git-zjx commented on June 22, 2024

如果没有主键的表，有一个普通索引，怎么回表?

没有主键的表，InnoDB会给默认创建一个Rowid做主键

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git-zjx avatar git-zjx commented on June 22, 2024

一个InnoDB引擎的表，数据量非常大，根据二级索引搜索会比主键搜索快？

只有使用覆盖索引时会

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git-zjx avatar git-zjx commented on June 22, 2024

非聚集索引上为什么叶子节点不是数据行的地址，而是主键 id？

这个叫作“堆组织表”，MyISAM 就是这样的，各有利弊。在修改了数据的位置的情况，InnoDB 这种模式会更方便些

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git-zjx avatar git-zjx commented on June 22, 2024

如果磁盘中的主键索引已经存储了这个表的全部数据的话，那常说的没走索引是遍历整个B+树还是其他地方还有整个表的数据呢？

就是遍历这个主键索引的意思

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git-zjx avatar git-zjx commented on June 22, 2024

InnoDB B+树主键索引的叶子节点存的是什么？

B+树的叶子节点是page （页），一个页里面可以存多个行

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git-zjx avatar git-zjx commented on June 22, 2024

非叶子节点存储大约 1200个是怎么算出来的？

整型 4 个字节，加上辅助数据差不多每个key占13字节，16k/13

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git-zjx avatar git-zjx commented on June 22, 2024

为什么树高20就是20个数据块？

每个叶子结点就是一个块，每个块包含两个数据，块之间通过链式方式链接。树高20的话，就要遍历20个块

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