[IMPALA-9963] Implement ds_kll_n() function

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.0.0
• Component/s: Backend
• Epic Link: unlabelled-IMPALA-9594
• Epic Color: ghx-label-11
• Assignee: Gabor Kaszab
• Reporter: Gabor Kaszab
• Created: 16/Jul/20 09:29
• Updated: 07/Aug/20 07:02
• Resolved: 07/Aug/20 07:02

Description

ds_kll_n() receives a serialized Apache DataSketches KLL sketch and returns how many values were fed into the sketch.
Returns a bigint.

Example:

select ds_kll_n(ds_kll_sketch(cast(int_col as float))) from table_name;
+------+
| _c0  |
+------+
| 6    |
+------+