//查询name不为空的用户，并且邮箱不为空的用户，年龄大于等于12

 @Test

 void selectBy01(){

 ​

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     wrapper

             .isNotNull("name") //name不为空的用户

             .isNotNull("email") //邮箱不为空的用户

             .ge("age",12); //年龄大于等于12

 ​

     userMapper.selectList(wrapper).forEach(System.out::println);

 }

//查询name为 "Jone" 的用户

 @Test

 void selectBy02(){

 ​

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     wrapper.eq("name","Jone"); //name为 "Jone" 的用户

 ​

     //查询一个数据，为多个用 selectList 或者 selectByMap

     User user = userMapper.selectOne(wrapper);

 ​

     System.out.println(user);

 }

 //查询 10 到 20 岁的用户数

 @Test

 void selectBy03(){

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     wrapper.between("age",10,20);

 ​

     Integer count = userMapper.selectCount(wrapper);

     //查询 10 到 20 岁的用户的结果数

 ​

     System.out.println(count);

 }

 @Test

 void selectLike01(){

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     wrapper

             .notLike("name","To") //名字不包含 To

             .like("name","o") //名字包含 o 的

             //左和右 左：%e   右：e%  两边：%e%

             //右查询

             .likeRight("email","test");

 ​

     List<Map<String, Object>> users = userMapper.selectMaps(wrapper);

     users.forEach(System.out::println);

 }

 @Test

 void selectLike02(){

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     wrapper

             //一个SQL语句写的子查询

             .inSql("id","select id from user where age<20");

 ​

     List<Object> users = userMapper.selectObjs(wrapper);

     users.forEach(System.out::println);

 }

@Test

 void selectLike03(){

     QueryWrapper<User> wrapper=new QueryWrapper<>();

     //降序排序

     wrapper.orderByDesc("id");

     //升序排序

     //wrapper.orderByAsc("id");

 ​

     List<User> users = userMapper.selectList(wrapper);

     users.forEach(System.out::println);

 }