拉链表

拉链表实现方式一：

ods层的user表

现在我们来看一下我们ods层的用户资料切片表的结构：

CREATE EXTERNAL TABLE ods.user ( 
  user_num STRING COMMENT '用户编号', 
  mobile STRING COMMENT '手机号码', 
  reg_date STRING COMMENT '注册日期' 
COMMENT '用户资料表' 
PARTITIONED BY (dt string) 
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' LINES TERMINATED BY '\n' 
STORED AS ORC 
LOCATION '/ods/user'; 
) 
ods层的user_update表

然后我们还需要一张用户每日更新表，前面已经分析过该如果得到这张表，现在我们假设它已经存在。

CREATE EXTERNAL TABLE ods.user_update ( 
  user_num STRING COMMENT '用户编号', 
  mobile STRING COMMENT '手机号码', 
  reg_date STRING COMMENT '注册日期' 
COMMENT '每日用户资料更新表' 
PARTITIONED BY (dt string) 
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' LINES TERMINATED BY '\n' 
STORED AS ORC 
LOCATION '/ods/user_update'; 
) 
拉链表

现在我们创建一张拉链表：

CREATE EXTERNAL TABLE dws.user_his ( 
  user_num STRING COMMENT '用户编号', 
  mobile STRING COMMENT '手机号码', 
  reg_date STRING COMMENT '用户编号', 
  t_start_date , 
  t_end_date 
COMMENT '用户资料拉链表' 
ROW FORMAT DELIMITED FIELDS TERMINATED BY '\t' LINES TERMINATED BY '\n' 
STORED AS ORC 
LOCATION '/dws/user_his'; 
) 

拉链表的实现：

INSERT OVERWRITE TABLE dws.user_his 
SELECT * FROM 
( 
    SELECT A.user_num, 
           A.mobile, 
           A.reg_date, 
           A.t_start_time, 
           CASE 
                WHEN A.t_end_time = '9999-12-31' AND B.user_num IS NOT NULL THEN '2017-01-01' 
                ELSE A.t_end_time 
           END AS t_end_time 
    FROM dws.user_his AS A 
    LEFT JOIN ods.user_update AS B 
    ON A.user_num = B.user_num 
UNION 
    SELECT C.user_num, 
           C.mobile, 
           C.reg_date, 
           '2017-01-02' AS t_start_time, 
           '9999-12-31' AS t_end_time 
    FROM ods.user_update AS C 
) AS T