Mybatis-Plus select不去查全部字段和去重

mybatis-plus select查詢語句默認是查全部字段，有兩種方法可以指定要查詢的字段

CREATE TABLE `user` (
  `id` bigint(20) NOT NULL COMMENT '主鍵',
  `name` varchar(30) DEFAULT NULL COMMENT '姓名',
  `age` int(11) DEFAULT NULL COMMENT '年齡',
  `email` varchar(50) DEFAULT NULL COMMENT '郵箱',
  `manager_id` bigint(20) DEFAULT NULL COMMENT '直屬上級id',
  `create_time` datetime DEFAULT NULL COMMENT '創建時間',
  PRIMARY KEY (`id`),
  KEY `manager_fk` (`manager_id`),
  CONSTRAINT `manager_fk` FOREIGN KEY (`manager_id`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

1、user表只需要查詢出name和age兩個字段的數據，可以使用queryWrapper的select()方法指定要查詢的字段

    @Test
    public void selectByWrapper10() {
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("name", "age").like("name", "雨");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

日志輸出sql：

DEBUG==> Preparing: SELECT name,age FROM user WHERE name LIKE ?
DEBUG==> Parameters: %雨%(String)
TRACE<== Columns: name, age
TRACE<== Row: 張雨琪, 31
TRACE<== Row: 劉紅雨, 31
DEBUG<== Total: 2

2、user表要查詢出除manager_id和create_time外其它所有字段的數據，同樣也是使用queryWrapper的select()方法

    @Test
    public void selectByWrapper11() {
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select(User.class, info -> !info.getColumn().equals("manager_id")
                && !info.getColumn().equals("create_time"));
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

日志輸出sql：

DEBUG==> Preparing: SELECT id,name,age,email FROM user
DEBUG==> Parameters:
TRACE<== Columns: id, name, age, email
TRACE<== Row: 1087982257332887553, 大boss, 40, [e-mail]
TRACE<== Row: 1088248166370832385, 王天風, 25, [e-mail]
TRACE<== Row: 1088250446457389058, 李藝偉, 28, [e-mail]
TRACE<== Row: 1094590409767661570, 張雨琪, 31, [e-mail]
TRACE<== Row: 1094592041087729666, 劉紅雨, 31, [e-mail]
DEBUG<== Total: 5

Mybatis plus實現Distinct去重功能

不啰嗦，上菜

	QueryWrapper queryWrapper = new QueryWrapper();
	queryWrapper.select("DISTINCT no,name").orderByAsc("no");
	return mapper.selectList(queryWrapper);
123

PS:
順便一提，指明查詢出后的結果輸出類型，可以參考如下：

	QueryWrapper<TablePo> queryWrapper = new QueryWrapper<>();
	queryWrapper.select("DISTINCT no,name").orderByAsc("no");
	return mapper.selectList(queryWrapper);