zkytech commented on PR #4423:
URL: https://github.com/apache/zeppelin/pull/4423#issuecomment-1193082009
>
To make it easier to join between different database. For example， join
between `mongodb` & `hive` & `mysql`, assuming that:
- hive has a user_info table with fields: `user_name`, `occupation_code`,
`region_code`
- mongo has a occupation_info table with fields: `occupation_code`,
`occupation_name`
- mysql has a region_info table with fields: `region_code`, `region_name`
I want to get data with these fields: `user_name`, `occupation_name`,
`region_name`
Without cross datasource query , I need to write spark scala code to load
mongo/mysql table to Spark DataFrame, it is a hard job to do this every time.
With cross datasource query, I can easily take these fields from mongodb and
mysql with only one sql query.
```sql
select
t1.user_name, t2.occupation_name, t3.region_name
from
hive_db.user_info as t1
left join
mongodb.user_db.occupation_info as t2
on
t1.occupation_code = t2.occupation_code
left join
mysql.another_userinfo_db.region_info as t3
on
t1.region_code = t3.region_code
```
This is a lightweight replacement for presto, easier to use for zeppelin
users .
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