[jira] [Commented] (KYLIN-1875) Kylin support SnowFlake schema

["liyang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KYLIN-1875?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15680172#comment-15680172 ] 

liyang commented on KYLIN-1875:
-------------------------------

Initial design, a {{Data Model}} consists of the following:

- one {{Root Fact Table}}
- multiple {{Fact Tables}}
- multiple {{Lookup Tables}}  (can fit in memory, typically < 300 MB)
- multiple {{Join Relationships}} that connect tables to the Root Fact Table directly or indirectly

During cube build

- All tables are joined together and then aggregated as the {{Cube}}
- Lookup tables, due to the small size, are also saved as {{Snapshots}}

Query and limitations

- Lookup tables can be queried independently from the Snapshots, ensures correct result
- Fact tables can only be queried from cube, which enforces the pre-calculated joint and aggregated result
-- *No raw records* limitation. This is the same as before.
-- For example, {{select * from F}} actually returns {{select * from F group by D1, D2, ..., Dn}}, where F is fact table, Dn are dimension columns.
-- *Enforced joint* limitation. Query on any fact table will enforce the joins of the whole model, since cube only stores pre-calculated joint result.
-- For example, {{select ... from F1}} will be executed as {{select ... from F1 join F2 ... join L1 join L2...}}, where Fn are fact tables, Ln are lookup tables.

> Kylin support SnowFlake schema
> ------------------------------
>
>                 Key: KYLIN-1875
>                 URL: https://issues.apache.org/jira/browse/KYLIN-1875
>             Project: Kylin
>          Issue Type: Improvement
>    Affects Versions: v1.5.2
>            Reporter: Rahul Choubey
>            Assignee: liyang
>




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