jiaan.geng created SPARK-32934:
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Summary: Support a new window frame could improve the performance
for NTH_VALUE,FIRST_VALUE,LAST_VALUE
Key: SPARK-32934
URL: https://issues.apache.org/jira/browse/SPARK-32934
Project: Spark
Issue Type: Sub-task
Components: SQL
Affects Versions: 3.1.0
Reporter: jiaan.geng
Spark SQL support some window function like NTH_VALUE,FIRST_VALUE and
LAST_VALUE
If we specify window frame like
{code:java}
UNBOUNDED PRECEDING AND CURRENT ROW
{code}
or
{code:java}
UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
{code}
We can elimate some calculations.
For example: if we execute the SQL show below:
{code:java}
SELECT NTH_VALUE(col,
2) OVER(ORDER BY rank UNBOUNDED PRECEDING
AND CURRENT ROW)
FROM tab;
{code}
The output for row number greater than 1, return the fixed value. otherwise,
return null. So we just calculate the value once and notice whether the row
number less than 2.
UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING is simpler.
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