在Spring Boot中整合Sharding-JDBC和MyBatis，以及实现分库分表的基本步骤如下：

1. 添加依赖：

   <dependency>
       <groupId>org.mybatis.spring.boot</groupId>
       <artifactId>mybatis-spring-boot-starter</artifactId>
       <version>2.2.0</version>
   </dependency>
   <dependency>
       <groupId>org.apache.shardingsphere</groupId>
       <artifactId>sharding-jdbc-spring-boot-starter</artifactId>
       <version>5.0.0-RC1</version>
   </dependency>
   

2. 配置数据源与分片规则（application.yml）：

   spring:
     shardingsphere:
       datasource:
         names: ds0,ds1
         ds0:
           type: com.zaxxer.hikari.HikariDataSource
           driver-class-name: com.mysql.jdbc.Driver
           url: jdbc:mysql://localhost:3306/db0
           username: root
           password: root
         ds1:
           type: com.zaxxer.hikari.HikariDataSource
           driver-class-name: com.mysql.jdbc.Driver
           url: jdbc:mysql://localhost:3306/db1
           username: root
           password: root
   
       sharding:
         tables:
           t_order:
             actual-data-nodes: ds${0..1}.t_order${0..1}
             table-strategy:
               inline:
                 sharding-column: user_id
                 algorithm-expression: t_order${user_id % 2}
   
     mybatis:
       mapper-locations: classpath:mapper/*.xml
       type-aliases-package: com.example.model
   

3. 创建实体类（如User.java）和对应的Mapper接口及XML文件（UserMapper.java & UserMapper.xml）。

4. 在XML映射文件中编写SQL语句，无需关心具体的数据库和表名，由Sharding-JDBC自动处理路由。

   <?xml version="1.0" encoding="UTF-8" ?>
   <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
   <mapper namespace="com.example.mapper.UserMapper">
   
       <select id="selectById" resultType="com.example.model.User">
           SELECT * FROM t_order WHERE user_id = #{userId}
       </select>
   
   </mapper>
   

5. 使用@Mapper注解将Mapper接口注入到Service或Controller中，并正常进行CRUD操作。

   @Service
   public class UserService {
   
       @Autowired
       private UserMapper userMapper;
   
       public User getUserById(Long userId) {
           return userMapper.selectById(userId);
       }
   }
   

通过上述配置和代码示例，Spring Boot项目成功整合了Sharding-JDBC和MyBatis，并实现了基于user_id的分库分表。当执行查询时，Sharding-JDBC会根据配置的策略将SQL请求路由到正确的数据库和表上。