为了支持Kylin中多表查询，一般是一个事实表关联多张维度表，并获取衍生维度，我们通过在Caravel Table中添加自定义字段，并对该字段定义一定规则的表达式(字段串常量)，提交到PyKylin之后，PyKylin解析该字符串常量，转换成与维度表关联的SQL查询并返回结果。
这里做法有些粗糙，但功能基本实现，你可以参考该思路做进一步的优化和修改。

这里以事实表AD_REPORT2为例，其中有维度ID字段AD_ID，在Kylin中构建Cube时候，通过INNER JOIN维度表AD_DIM来获取维度名称AD_NAME。

在Caravel的AD_REPORT2中添加字段ad_name，

caravel

该字段表达式为字符串常量：
‘$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|$’

字符串以$开头和结尾，以|分隔。
INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = ad_id)
定义了维度表、JOIN类型、ON条件，该字符串会直接添加到原始SQL中，作为JOIN子句；
在维度表中的字段前面加上为了和事实表中的字段区分而不用考虑表的别名。
b.__ad_name
定义了使用该字段作为最终的字段取值。

当选择ad_name作为维度查询时，Caravel提交给PyKylin的SQL语句为：

SELECT '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre> AS ad_name,
SUM(imp_pv) AS sum__imp_pv
FROM liuxiaowen.AD_REPORT2
WHERE pt >= '2015-06-13'
AND pt <= '2016-06-13'
GROUP BY '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre>
ORDER BY SUM(imp_pv) DESC
LIMIT 50

</pre>

PyKylin经过转换后提交给Kylin的SQL语句为：

SELECT b.__ad_name as ad_name,
SUM(imp_pv) AS sum__imp_pv
FROM liuxiaowen.ad_report2
inner join (SELECT ad_id AS __ad_id,ad_name AS __ad_name FROM liuxiaowen.ad_dim) AS b
ON (ad_id = __ad_id)
WHERE pt >= '2015-06-13' AND pt <= '2016-06-13'
GROUP BY b.__ad_name
ORDER BY SUM(imp_pv) DESC

</pre>

对于时间序列类的图表，Caravel提交给PyKylin的SQL语句为：

SELECT '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre> AS ad_name,
pt AS _timestamp,
SUM(imp_pv) AS sum__imp_pv
FROM liuxiaowen.AD_REPORT2
JOIN (
SELECT '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre> AS __ad_name
FROM liuxiaowen.AD_REPORT2
WHERE pt >= '2015-06-13' AND pt <= '2016-06-13'
GROUP BY '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre>
ORDER BY SUM(imp_pv) DESC
LIMIT 50
) AS anon_1
ON '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre> = __ad_name
WHERE pt >= '2015-06-13' AND pt <= '2016-06-13'
GROUP BY '$|INNER JOIN (select ad_id as __ad_id,ad_name as __ad_name from LIUXIAOWEN.AD_DIM) as b ON (ad_id = __ad_id)|b.__ad_name|/pre>, pt
ORDER BY SUM(imp_pv) DESC
LIMIT 50000

</pre>

PyKylin经过优化后的SQL语句为：

SELECT b.__ad_name AS ad_name,
pt AS _timestamp,
SUM(imp_pv) AS sum__imp_pv
FROM liuxiaowen.ad_report2
inner join (SELECT ad_id AS __ad_id,ad_name AS __ad_name FROM liuxiaowen.ad_dim) AS b
ON (ad_id = __ad_id)
WHERE pt >= '2015-06-13' AND pt <= '2016-06-13'
GROUP by b.__ad_name, pt
ORDER by sum(imp_pv) desc
limit 50

</pre>

该配置方法对于关联一张维度表获取多个字段，以及关联多张维度表获取多个维度字段同样适用，只需要在Caravel Table中添加多个字段，表达式的写法一样即可。

另外，该修改只针对数据源类型为kylin，对于Caravel使用其他数据源不受影响。

Enjoy it!

20160812更新：

很多网友在按照上面的方法（基于源码离线安装）安装之后，都遇到了js无法正常加载，页面无法正常显示的问题，该问题是由于node/npm环境未正确安装而导致的。

解决方法请参考官方说明 https://github.com/airbnb/caravel/blob/master/CONTRIBUTING.md#setting-up-the-node–npm-javascript-environment

或者 http://www.cnblogs.com/kevin19900306/p/5701401.html

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转载请注明：lxw的大数据田地 » 开源OLAP+数据可视化工具–For Apache Kylin