Gabor Kaszab created IMPALA-9962:
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Summary: Implement ds_kll_quantiles() function
Key: IMPALA-9962
URL: https://issues.apache.org/jira/browse/IMPALA-9962
Project: IMPALA
Issue Type: Improvement
Components: Backend
Reporter: Gabor Kaszab
Requirements for ds_kll_quantiles()
- Receives a serialized KLL sketch in BINARY type (in Impala it can be STRING
as long as we don't have BINARY) as first parameter.
- Receives one or more double values to represent the quantile points.
- In Hive the return type is an array of doubles. However, Impala can't return
complex types from functions at this point so we have to find some alternative
approaches to implement this function.
** One would be to return as many columns as many quantile points were given.
** Another approach is to create a comma separated string from the results of
this function and return that string instead of an array.
Hive example:
{code:java}
select ds_kll_quantiles(ds_kll_sketch(cast(int_col as float)), 0, 0.1, 0.5, 1)
from table_name
+--------------------+
| _c0 |
+--------------------+
| [1.0,1.0,1.0,1.0] |
+--------------------+
{code}
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