[HIVE-6942] Explanation of GROUPING__ID is confusing

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Documentation
• Assignee: Unassigned
• Reporter: chris schrader
• Created: 21/Apr/14 20:22
• Updated: 21/Apr/14 20:22

Description

The explanation given for GROUPING__ID in enhanced aggregations is very incomplete and confusing based on the example. Documentation here:

https://cwiki.apache.org/confluence/display/Hive/Enhanced+Aggregation,+Cube,+Grouping+and+Rollup#EnhancedAggregation,Cube,GroupingandRollup-Grouping__IDfunction

It would be far easier to understand if the "bit vector" were explained better along side the examples given. IE, also explain identifying each column in terms of the binary number it returns and then show it converted to decimal. In the examples provided, the binary equivalent of the grouping ID's for the first example would be 1,11,11 representing the columns included in aggregation. The documentation is very confusing without this clear connection between creating a binary number that gets converted (just referring to it as a "bitvector" isn't sufficient to the average user).