[大数据]mybatis-plus的查找操作的实现

1.查找操作实现：
1.1 无条件的查找

List<Student> list =  studentService.list();

1.2
1.2.1根据多个Id查询

List<Integer> ids = Arrays.asList(202101,202102);
List<Student> list = studentService.listByIds(ids);

1.2.2
单个id:

studentService.getById(202101)

1.3 根据条件查询
1.3.1实现下面的sql语句：

select * from student where student_name ='aaaa';

mybatis-plus实现：

QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.eq("student_name",'aaaa');
List<Student> list = studentService.list(wrapper);

1.3.2 多条件的查询(and)

select * from student where student_name="a" and student_id=1;

mybatis-plus实现：

QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.eq("student_id",1).eq("student_name","a");
List<Student> list = studentService.list(wrapper);

1.3.3 多条件查询（or）

select * from student where student_naem='a' or student_id=1;

mybatis-plus实现：

QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.eq("student_id",1).or().eq("student_name","a");
List<Student> list = studentService.list(wrapper);

1.4 模糊查询(多条件如上)

select * from student where student_naem like 'a' 

mybatis-plus实现：

QueryWrapper<Student> wrapper = new QueryWrapper<>();
wrapper.like("student_name","a");
List<Student> list = studentService.list(wrapper);