MyBatis树形结构查询的实现示例

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for area
-- ----------------------------
DROP TABLE IF EXISTS `area`;
CREATE TABLE `area` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'PK',
  `area_name` varchar(50) NOT NULL COMMENT '地区名称',
  `parent_id` int(11) NOT NULL COMMENT '父Id',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7668 DEFAULT CHARSET=utf8 COMMENT='地区表';

-- ----------------------------
-- Records of area
-- ----------------------------
INSERT INTO `area` VALUES ('1', '广东省', '0');
INSERT INTO `area` VALUES ('2', '深圳市', '1');
INSERT INTO `area` VALUES ('3', '广州市', '1');
INSERT INTO `area` VALUES ('4', '湖南省', '0');
INSERT INTO `area` VALUES ('5', '长沙市', '4');
INSERT INTO `area` VALUES ('6', '株洲市', '4');

public class Area {
    private Integer id;

    private String areaName;

    private Integer parentId;

    List<Area> children;

   //getter setter
}

SELECT
        t_top.id AS id1,
        t_top.area_name AS area_name1,
        t_top.parent_id AS parent_id1,
        t_second.id AS id2,
        t_second.area_name AS area_name2,
        t_second.parent_id AS parent_id2
    FROM
        (
            SELECT
                id,
                area_name,
                parent_id
            FROM
                area
            WHERE
                parent_id = 0
        ) AS t_top
    INNER JOIN (
        SELECT
            id,
            area_name,
            parent_id
        FROM
            area
        WHERE
            parent_id IN (
                SELECT
                    id
                FROM
                    area
                WHERE
                    parent_id = 0
            )
    ) AS t_second ON t_top.id = t_second.parent_id

  <resultMap id="TreeResultMap" type="com.domain.Area" >
    <id column="id1" property="id" jdbcType="INTEGER" />
    <result column="area_name1" property="areaName" jdbcType="VARCHAR" />
    <result column="parent_id1" property="parentId" jdbcType="INTEGER" />
    <collection property="children" ofType="com.domain.Area">
      <id column="id2" property="id" jdbcType="INTEGER" />
      <result column="area_name2" property="areaName" jdbcType="VARCHAR" />
      <result column="parent_id2" property="parentId" jdbcType="INTEGER" />
    </collection>
  </resultMap>