在Hive上实现SCD

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://cloud.tencent.com/developer/article/1433192

一、问题提出

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     官方一直称Hive是Hadoop数据仓库解决方案。既然是数据仓库就离不开多维、CDC、SCD这些概念，于是尝试了一把在Hive上实现SCD1和SCD2。这有两个关键点，一个是行级更新，一个是生成代理键。行级更新hive本身就是支持的，但需要一些配置，还有一些限制。具体可参考[http://blog.csdn.net/wzy0623/article/details/51483674](http://blog.csdn.net/wzy0623/article/details/51483674)。生成代理键在RDBMS上一般都用自增序列。Hive也有一些对自增序列的支持，本实验分别使用了窗口函数ROW_NUMBER()和hive自带的UDFRowSequence实现生成代理键。

二、软件版本

Hadoop 2.7.2

Hive 2.0.0

三、实验步骤

1. 准备初始数据文件a.txt，内容如下：

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1,张三,US,CA
2,李四,US,CB
3,王五,CA,BB
4,赵六,CA,BC
5,老刘,AA,AA

1. 用ROW_NUMBER()方法实现初始装载和定期装载

（1）建立初始装载脚本init_row_number.sql，内容如下：

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USE test;

-- 建立过渡表
DROP TABLE IF EXISTS tbl_stg;
CREATE TABLE tbl_stg (
    id INT,
    name STRING,
    cty STRING,
    st STRING
)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';

-- 建立维度表
DROP TABLE IF EXISTS tbl_dim;
CREATE TABLE tbl_dim (
    sk INT,
    id INT,
    name STRING,
    cty STRING,
    st STRING,
    version INT,
    effective_date DATE,
    expiry_date DATE)
CLUSTERED BY (id) INTO 8 BUCKETS
STORED AS ORC TBLPROPERTIES ('transactional'='true');

-- 向过渡表加载初始数据
LOAD DATA LOCAL INPATH '/home/grid/BigDataDWTest/a.txt' INTO TABLE tbl_stg;

-- 向维度表装载初始数据
INSERT INTO tbl_dim
SELECT
    ROW_NUMBER() OVER (ORDER BY tbl_stg.id)   t2.sk_max,
    tbl_stg.*,
    1,
    CAST('1900-01-01' AS DATE),
    CAST('2200-01-01' AS DATE)
from tbl_stg CROSS JOIN (SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

（2）执行初始装载

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hive -S -f /home/grid/BigDataDWTest/init_row_number.sql

（3）修改数据文件a.txt，内容如下：

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1,张,U,C
3,王五,CA,BB
4,赵六,AC,CB
5,刘,AA,AA
6,老杨,DD,DD

说明：

1. 新增了第6条数据
2. 删除了第2条数据
3. 修改了第1条数据的name列、cty列和st列（name列按SCD2处理，cty列和st列按SCD1处理）
4. 修改了第4条数据的cty列和st列（按SCD1处理）
5. 修改了第5条数据的name列（按SCD2处理）

（4）建立定期装载脚本scd_row_number.sql，内容如下：

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USE test;

-- 设置日期变量
SET hivevar:pre_date = DATE_ADD(CURRENT_DATE(),-1);
SET hivevar:max_date = CAST('2200-01-01' AS DATE);

-- 向过渡表加载更新后的数据
LOAD DATA LOCAL INPATH '/home/grid/BigDataDWTest/a.txt' OVERWRITE INTO TABLE tbl_stg;

-- 向维度表装载更新后的数据
-- 设置已删除记录和SCD2的过期
UPDATE tbl_dim
SET expiry_date = ${hivevar:pre_date}
WHERE sk IN
(SELECT a.sk FROM (
SELECT sk,id,name FROM tbl_dim WHERE expiry_date = ${hivevar:max_date}) a LEFT JOIN tbl_stg b ON a.id=b.id
WHERE b.id IS NULL OR a.name<>b.name);

-- 处理SCD2新增行
INSERT INTO tbl_dim
SELECT
    ROW_NUMBER() OVER (ORDER BY t1.id)   t2.sk_max,
    t1.id,
    t1.name,
    t1.cty,
    t1.st,
    t1.version,
    t1.effective_date,
    t1.expiry_date
FROM
(
SELECT
    t2.id id,
    t2.name name,
    t2.cty cty,
    t2.st st,
    t1.version   1 version,
    ${hivevar:pre_date} effective_date,
    ${hivevar:max_date} expiry_date
FROM tbl_dim t1 INNER JOIN tbl_stg t2
ON t1.id=t2.id AND t1.name<>t2.name AND t1.expiry_date = ${hivevar:pre_date}
LEFT JOIN tbl_dim t3 ON T1.id = t3.id AND t3.expiry_date = ${hivevar:max_date}
WHERE t3.sk IS NULL) t1
CROSS JOIN
(SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

-- 处理SCD1
-- 因为hive的update还不支持子查询，所以这里使用了一个临时表存储需要更新的记录，用先delete再insert代替update
-- 因为SCD1本身就不保存历史数据，所以这里更新维度表里的所有cty或st改变的记录，而不是仅仅更新当前版本的记录
DROP TABLE IF EXISTS tmp;
CREATE TABLE tmp AS
SELECT a.sk,a.id,a.name,b.cty,b.st,a.version,a.effective_date,a.expiry_date FROM tbl_dim a, tbl_stg b
WHERE a.id=b.id AND (a.cty <> b.cty OR a.st <> b.st);
DELETE FROM tbl_dim WHERE sk IN (SELECT sk FROM tmp);
INSERT INTO tbl_dim SELECT * FROM tmp;

-- 处理新增记录
INSERT INTO tbl_dim
SELECT
    ROW_NUMBER() OVER (ORDER BY t1.id)   t2.sk_max,
    t1.id,
    t1.name,
    t1.cty,
    t1.st,
    1,
    ${hivevar:pre_date},
    ${hivevar:max_date}
FROM
(
SELECT t1.* FROM tbl_stg t1 LEFT JOIN tbl_dim t2 ON t1.id = t2.id
WHERE t2.sk IS NULL) t1
CROSS JOIN
(SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

（5）执行定期装载

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hive -S -f /home/grid/BigDataDWTest/scd_row_number.sql

查询维度表结果如图1所示。

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select * from tbl_dim order by id,version;

图1

（6）再次执行定期装载，维度表的数据没有变化

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hive -S -f /home/grid/BigDataDWTest/scd_row_number.sql

1. 用UDFRowSequence方法实现初始装载和定期装载 实验过程和ROW_NUMBER()方法基本一样，只是先要将hive-contrib-2.0.0.jar传到HDFS上，否则会报错。

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hadoop dfs -put /home/grid/hive/lib/hive-contrib-2.0.0.jar /user

初始装载脚本init_UDFRowSequence.sql，内容如下：

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USE test;

ADD JAR hdfs:///user/hive-contrib-2.0.0.jar;
CREATE TEMPORARY FUNCTION row_sequence as 'org.apache.hadoop.hive.contrib.udf.UDFRowSequence';

-- 建立过渡表
DROP TABLE IF EXISTS tbl_stg;
CREATE TABLE tbl_stg (
    id INT,
    name STRING,
    cty STRING,
    st STRING
)
ROW FORMAT DELIMITED FIELDS TERMINATED BY ',';

-- 建立维度表
DROP TABLE IF EXISTS tbl_dim;
CREATE TABLE tbl_dim (
    sk INT,
    id INT,
    name STRING,
    cty STRING,
    st STRING,
    version INT,
    effective_date DATE,
    expiry_date DATE)
CLUSTERED BY (id) INTO 8 BUCKETS
STORED AS ORC TBLPROPERTIES ('transactional'='true');

-- 向过渡表加载初始数据
LOAD DATA LOCAL INPATH '/home/grid/BigDataDWTest/a.txt' INTO TABLE tbl_stg;

-- 向维度表装载初始数据
INSERT INTO tbl_dim
SELECT
    t2.sk_max   row_sequence(),
    tbl_stg.*,
    1,
    CAST('1900-01-01' AS DATE),
    CAST('2200-01-01' AS DATE)
from tbl_stg CROSS JOIN (SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

定期装载脚本scd_UDFRowSequence.sql，内容如下：

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USE test;

ADD JAR hdfs:///user/hive-contrib-2.0.0.jar;
CREATE TEMPORARY FUNCTION row_sequence as 'org.apache.hadoop.hive.contrib.udf.UDFRowSequence';

-- 设置日期变量
SET hivevar:pre_date = DATE_ADD(CURRENT_DATE(),-1);
SET hivevar:max_date = CAST('2200-01-01' AS DATE);

-- 向过渡表加载更新后的数据
LOAD DATA LOCAL INPATH '/home/grid/BigDataDWTest/a.txt' OVERWRITE INTO TABLE tbl_stg;

-- 向维度表装载更新后的数据
-- 设置已删除记录和SCD2的过期
UPDATE tbl_dim
SET expiry_date = ${hivevar:pre_date}
WHERE sk IN
(SELECT a.sk FROM (
SELECT sk,id,name FROM tbl_dim WHERE expiry_date = ${hivevar:max_date}) a LEFT JOIN tbl_stg b ON a.id=b.id
WHERE b.id IS NULL OR a.name<>b.name);

-- 处理SCD2新增行
INSERT INTO tbl_dim
SELECT
    t2.sk_max   row_sequence(),
    t1.id,
    t1.name,
    t1.cty,
    t1.st,
    t1.version,
    t1.effective_date,
    t1.expiry_date
FROM
(
SELECT
    t2.id id,
    t2.name name,
    t2.cty cty,
    t2.st st,
    t1.version   1 version,
    ${hivevar:pre_date} effective_date,
    ${hivevar:max_date} expiry_date
FROM tbl_dim t1 INNER JOIN tbl_stg t2
ON t1.id=t2.id AND t1.name<>t2.name AND t1.expiry_date = ${hivevar:pre_date}
LEFT JOIN tbl_dim t3 ON T1.id = t3.id AND t3.expiry_date = ${hivevar:max_date}
WHERE t3.sk IS NULL) t1
CROSS JOIN
(SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

-- 处理SCD1
-- 因为hive的update还不支持子查询，所以这里使用了一个临时表存储需要更新的记录，用先delete再insert代替update
-- 因为SCD1本身就不保存历史数据，所以这里更新维度表里的所有cty或st改变的记录，而不是仅仅更新当前版本的记录
DROP TABLE IF EXISTS tmp;
CREATE TABLE tmp AS
SELECT a.sk,a.id,a.name,b.cty,b.st,a.version,a.effective_date,a.expiry_date FROM tbl_dim a, tbl_stg b
WHERE a.id=b.id AND (a.cty <> b.cty OR a.st <> b.st);
DELETE FROM tbl_dim WHERE sk IN (SELECT sk FROM tmp);
INSERT INTO tbl_dim SELECT * FROM tmp;

-- 处理新增记录
INSERT INTO tbl_dim
SELECT
    t2.sk_max   row_sequence(),
    t1.id,
    t1.name,
    t1.cty,
    t1.st,
    1,
    ${hivevar:pre_date},
    ${hivevar:max_date}
FROM
(
SELECT t1.* FROM tbl_stg t1 LEFT JOIN tbl_dim t2 ON t1.id = t2.id
WHERE t2.sk IS NULL) t1
CROSS JOIN
(SELECT COALESCE(MAX(sk),0) sk_max FROM tbl_dim) t2;

参考：

http://blog.csdn.net/wzy0623/article/details/49616643

http://www.remay.com.br/blog/hdp-2-2-how-to-create-a-surrogate-key-on-hive/

http://www.aboutechnologies.com/2016/02/hive-auto-increment-column.html

内容分发网络CDN hive http hadoop

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