[Kernel]Implement substring expression in delta kernel library #4001
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huan233usc
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Which Delta project/connector is this regarding?
Description
Implements substring expression. This is 2/n for addressing #2539 (i.e. data skipping of startwith depends on substring expression, see[1] for spark's code pointer), the first part is implemented in #3991.
[1]https://github.com/delta-io/delta/blob/master/spark/src/main/scala/org/apache/spark/sql/delta/stats/DataSkippingReader.scala#L557-L561
How was this patch tested?
Added e2e test cases, the expected result are generated using spark, e.g.
WITH t(x) AS
(SELECT null union all select "one" union all select "two" union all select "three" union all select "four" union all select null union all select null union all select "seven" union all select "eight")
select substring(x,-100,98) from t
substring(x,-100,98)
null
o
t
thr
fo
null
null
sev
eig
Does this PR introduce any user-facing changes?
No