<dependency>    <groupId>com.baomidou</groupId>    <artifactId>mybatis-plus-boot-starter</artifactId>    <version>3.4.3</version></dependency>

#2.配置相关信息spring:  datasource:    driver-class-name: com.mysql.cj.jdbc.Driver    url: jdbc:mysql://localhost:3306/mp    username: root    password: root      mybatis-plus:  configuration:    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl     # 日志实现类  -->打印sql

public interface UserMapper extends BaseMapper<User> {
}

@Test    void select() {        //1、查询所有,不加条件去查询        userMapper.selectList(null).forEach(System.out::println);       //forEach遍历打印
        //2、查询所有,加条件去查询            //2.1、new QueryWrapper        QueryWrapper queryWrapper1 = new QueryWrapper();            //2.2、设置条件        queryWrapper1.eq("age", 20);        /**         * lt           #小于         * gt       #大于         * ne       #不等于         * eq       #等于         * le           #小于等于         * ge       #大于等于         * between      #between         * like like    模糊查询        #likeLeft 左模糊  likeRight 右模糊         * isNull         * isNotNull         * in                         #inSql in sql语句         * notIn         * orderBy                  #排序 ASC DESC 升序降序         * orderByDesc         */        userMapper.selectList(queryWrapper1).forEach(System.out::println);
        //3、多条件去查询        QueryWrapper queryWrapper2 = new QueryWrapper();            //3.1、设置多条件            Map<String,Object> map = new HashMap<>();            map.put("age",20);            map.put("name","张三");            //3.2、map放进queryWrapper        queryWrapper2.allEq(map);
        //byId        User user = userMapper.selectById(1);        System.out.println(user);
        //byBatchIds        userMapper.selectBatchIds(Arrays.asList(1,2,3)).forEach(System.out::println);       //Arrays.asList(1,2,3)是一个数组，把数组转换成list集合
        //通过map条件查询        //map只能是一个条件，不能是多个条件        Map<String,Object> map1 = new HashMap<>();        map1.put("age",20);        map1.put("name","张三");        userMapper.selectByMap(map).forEach(System.out::println);
        //4、分组查询        QueryWrapper queryWrapper3 = new QueryWrapper();        queryWrapper3.gt("age",20);        System.out.println(userMapper.selectCount(queryWrapper3));
        //将查询结果放入map中        userMapper.selectMaps(queryWrapper1).forEach(System.out::println);
        //分页查询        //1、配置类paginationInterceptor        //2、设置分页参数        Page<User> page = new Page<>(1,3);      //当前页，每页显示条数2        Page<User> userPage = userMapper.selectPage(page, null);//分页参数，查询条件
        System.out.println(userPage.getCurrent());      //当前页        System.out.println(userPage.getSize());     //每页显示条数
        userPage.getRecords().forEach(System.out::println);     //查询结果

        //封装到map中        Page<Map<String,Object>> mapPage = new Page<>(1,3);     //分页参数，查询条件        userMapper.selectMapsPage(mapPage, null).getRecords().forEach(System.out::println);     //查询结果
        //查询所有，只输出id        userMapper.selectObjs(null).forEach(System.out::println);     //查询结果
        //查询一个        System.out.println(userMapper.selectOne(null));     //查询结果
    }

mybatis-plus:  global-config:    db-config:      table-prefix: tb_    #设置所有表的通用前缀名称为tbl_