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case when supports NULL constant#2197

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alamb merged 3 commits intoapache:masterfrom
WinkerDu:master-case-when-null
Apr 13, 2022
Merged

case when supports NULL constant#2197
alamb merged 3 commits intoapache:masterfrom
WinkerDu:master-case-when-null

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@WinkerDu WinkerDu commented Apr 10, 2022 •
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Which issue does this PR close?

Closes #1189.

Rationale for this change

df case when expression cannot take NULL constant, like

> select CASE WHEN NULL THEN 'foo' ELSE 'bar' END;
thread 'main' panicked at 'WHEN expression did not return a BooleanArray', datafusion/src/physical_plan/expressions/case.rs:381:18
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Postgres:

# select case null when null then 'foo' else 'bar' end;
 case 
------
 bar
(1 row)

What changes are included in this PR?

For when expression without case expression, treat NULL as false before down cast to BooleanArray

Are there any user-facing changes?

No.

@WinkerDu WinkerDu changed the title case .. when .. supports NULL constants case when supports NULL constant Apr 10, 2022
@WinkerDu WinkerDu mentioned this pull request Apr 10, 2022
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WinkerDu commented Apr 11, 2022 •
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cc @yjshen @Dandandan @alamb, please have a review, thank you.

yjshen
yjshen reviewed Apr 11, 2022
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It seems the type-coercion suggested in the issue is not used. Cc @alamb.

yjshen
yjshen reviewed Apr 11, 2022
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WinkerDu commented Apr 11, 2022

cc @yjshen @alamb another commit pushed, PTAL, thank you.

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alamb approved these changes Apr 13, 2022
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Thank you @WinkerDu

datafusion/physical-expr/src/expressions/case.rs
.evaluate_selection(batch, &remainder)?;
// Treat 'NULL' as false value
let when_value = match when_value {
ColumnarValue::Scalar(value) if value.is_null() => {
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This is a reasonable solution I think -- ideally we would have been able to coerce this value into a ColumnarValue::Scalar(ScalarValue::Boolean(None)) at some earlier point.

However, I think this special case is reasonable (and the test coverage is nice) so 👍 from me

@alamb alamb merged commit d81657d into apache:master Apr 13, 2022
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WinkerDu commented Apr 13, 2022

@alamb @yjshen thank you both!

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alamb commented Apr 13, 2022

Thank you @WinkerDu

@WinkerDu WinkerDu deleted the master-case-when-null branch April 17, 2022 17:16
ovr pushed a commit to cube-js/arrow-datafusion that referenced this pull request Aug 15, 2022
@WinkerDu @ovr
case when supports NULL constant (apache#2197)
c20aad6 
* case when support  literal

* fmt fix

* code clean

Co-authored-by: duripeng <[email protected]>
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CASE expr with NULL literals panics 'WHEN expression did not return a BooleanArray'

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