字节面试题： Mysql索引结构，为什么要用b+树？

import java.util.Arrays;

class BPlusTreeNode {
    int[] keys;
    int[] values;
    BPlusTreeNode[] children;
    int numKeys;
    boolean leaf;

    BPlusTreeNode(int order, boolean leaf) {
        this.keys = new int[order];
        this.values = new int[order];
        this.children = new BPlusTreeNode[order + 1];
        this.numKeys = 0;
        this.leaf = leaf;
    }
}

public class BPlusTree {
    private BPlusTreeNode root;
    private int order;

    public BPlusTree(int order) {
        this.order = order;
        this.root = new BPlusTreeNode(order, true);
    }

    public void insert(int key, int value) {
        if (root.numKeys == order - 1) {
            BPlusTreeNode newRoot = new BPlusTreeNode(order, false);
            newRoot.children[0] = root;
            splitChild(newRoot, 0);
            root = newRoot;
            insertNonFull(root, key, value);
        } else {
            insertNonFull(root, key, value);
        }
    }

    private void insertNonFull(BPlusTreeNode node, int key, int value) {
        int i = node.numKeys - 1;
        if (node.leaf) {
            while (i >= 0 && key < node.keys[i]) {
                node.keys[i + 1] = node.keys[i];
                node.values[i + 1] = node.values[i];
                i--;
            }
            node.keys[i + 1] = key;
            node.values[i + 1] = value;
            node.numKeys++;
        } else {
            while (i >= 0 && key < node.keys[i]) {
                i--;
            }
            i++;
            if (node.children[i].numKeys == order - 1) {
                splitChild(node, i);
                if (key > node.keys[i]) {
                    i++;
                }
            }
            insertNonFull(node.children[i], key, value);
        }
    }

    private void splitChild(BPlusTreeNode parentNode, int childIndex) {
        BPlusTreeNode child = parentNode.children[childIndex];
        BPlusTreeNode newChild = new BPlusTreeNode(order, child.leaf);
        newChild.numKeys = order / 2;
        for (int j = 0; j < order / 2; j++) {
            newChild.keys[j] = child.keys[j + order / 2];
            newChild.values[j] = child.values[j + order / 2];
        }
        if (!child.leaf) {
            for (int j = 0; j < order / 2 + 1; j++) {
                newChild.children[j] = child.children[j + order / 2];
            }
        }
        child.numKeys = order / 2;
        for (int j = parentNode.numKeys - 1; j >= childIndex; j--) {
            parentNode.keys[j + 1] = parentNode.keys[j];
            parentNode.values[j + 1] = parentNode.values[j];
        }
        parentNode.keys[childIndex] = child.keys[order / 2 - 1];
        parentNode.values[childIndex] = child.values[order / 2 - 1];
        for (int j = parentNode.numKeys; j > childIndex + 1; j--) {
            parentNode.children[j + 1] = parentNode.children[j];
        }
        parentNode.children[childIndex + 1] = newChild;
        parentNode.numKeys++;
    }

    public void printTree() {
        printTree(root, 0);
    }

    private void printTree(BPlusTreeNode node, int level) {
        if (node != null) {
            System.out.println("Level " + level + ": " + Arrays.toString(node.keys));
            for (int i = 0; i <= node.numKeys; i++) {
                printTree(node.children[i], level + 1);
            }
        }
    }

    public static void main(String[] args) {
        BPlusTree bPlusTree = new BPlusTree(3);
        bPlusTree.insert(1, 10);
        bPlusTree.insert(2, 20);
        bPlusTree.insert(3, 30);
        bPlusTree.insert(4, 40);
        bPlusTree.insert(5, 50);
        bPlusTree.insert(6, 60);
        bPlusTree.printTree();
    }
}

-- 创建商品表
CREATE TABLE Products (
    ProductID INT PRIMARY KEY,
    ProductName VARCHAR(100) NOT NULL,
    Category VARCHAR(50),
    Price DECIMAL(10, 2) NOT NULL
);

-- 创建B+树索引
CREATE INDEX idx_ProductName ON Products(ProductName);
CREATE INDEX idx_Category ON Products(Category);
CREATE INDEX idx_Price ON Products(Price);

-- 创建用户关系表
CREATE TABLE UserRelationships (
    UserID INT PRIMARY KEY,
    Following INT,
    Followers INT
);

-- 创建B+树索引
CREATE INDEX idx_UserID ON UserRelationships(UserID);
CREATE INDEX idx_Following ON UserRelationships(Following);
CREATE INDEX idx_Followers ON UserRelationships(Followers);

-- 创建快递信息表
CREATE TABLE DeliveryInfo (
    TrackingNumber VARCHAR(20) PRIMARY KEY,
    ShippingAddress VARCHAR(100),
    DeliveryAddress VARCHAR(100)
);

-- 创建B+树索引
CREATE INDEX idx_TrackingNumber ON DeliveryInfo(TrackingNumber);
CREATE INDEX idx_ShippingAddress ON DeliveryInfo(ShippingAddress);
CREATE INDEX idx_DeliveryAddress ON DeliveryInfo(DeliveryAddress);

-- 创建客户账户表
CREATE TABLE CustomerAccount (
    CustomerID INT PRIMARY KEY,
    AccountType VARCHAR(20),
    Balance DECIMAL(10, 2)
);

-- 创建交易信息表
CREATE TABLE TransactionInfo (
    TransactionID INT PRIMARY KEY,
    CustomerID INT,
    TransactionAmount DECIMAL(10, 2),
    TransactionTime TIMESTAMP,
    FOREIGN KEY (CustomerID) REFERENCES CustomerAccount(CustomerID)
);

-- 创建B+树索引
CREATE INDEX idx_CustomerID ON CustomerAccount(CustomerID);
CREATE INDEX idx_AccountType ON CustomerAccount(AccountType);
CREATE INDEX idx_TransactionTime ON TransactionInfo(TransactionTime);