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move type coercion for case when expr #3676

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Merged
liukun4515 merged 4 commits into from
Oct 4, 2022
Merged

move type coercion for case when expr #3676

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support type coercion in logical phase and remove it in the physical …
liukun4515 Oct 1, 2022
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liukun4515 Oct 4, 2022
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liukun4515 Oct 4, 2022
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liukun4515 Oct 4, 2022
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52 changes: 26 additions & 26 deletions datafusion/core/tests/sql/expr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,25 +152,25 @@ async fn case_expr_with_null() -> Result<()> {
let actual = execute_to_batches(&ctx, sql).await;

let expected = vec![
"+------------------------------------------------+",
"| CASE WHEN #a.b IS NULL THEN NULL ELSE #a.b END |",
"+------------------------------------------------+",
"| |",
"| 3 |",
"+------------------------------------------------+",
"+----------------------------------------------+",
"| CASE WHEN a.b IS NULL THEN NULL ELSE a.b END |",
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@alamb alamb Oct 2, 2022

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this looks like an improvement but I don't understand the change

"+----------------------------------------------+",
"| |",
"| 3 |",
"+----------------------------------------------+",
];
assert_batches_eq!(expected, &actual);

let sql = "select case when b is null then null else b end from (select a,b from (values (1,1),(2,3)) as t (a,b)) a;";
let actual = execute_to_batches(&ctx, sql).await;

let expected = vec![
"+------------------------------------------------+",
"| CASE WHEN #a.b IS NULL THEN NULL ELSE #a.b END |",
"+------------------------------------------------+",
"| 1 |",
"| 3 |",
"+------------------------------------------------+",
"+----------------------------------------------+",
"| CASE WHEN a.b IS NULL THEN NULL ELSE a.b END |",
"+----------------------------------------------+",
"| 1 |",
"| 3 |",
"+----------------------------------------------+",
];
assert_batches_eq!(expected, &actual);

Expand All @@ -184,27 +184,27 @@ async fn case_expr_with_nulls() -> Result<()> {
let actual = execute_to_batches(&ctx, sql).await;

let expected = vec![
"+--------------------------------------------------------------------------------------------------------------------------+",
"| CASE WHEN #a.b IS NULL THEN NULL WHEN #a.b < Int64(3) THEN NULL WHEN #a.b >= Int64(3) THEN #a.b + Int64(1) ELSE #a.b END |",
"+--------------------------------------------------------------------------------------------------------------------------+",
"| |",
"| |",
"| 4 |",
"+--------------------------------------------------------------------------------------------------------------------------+"
"+---------------------------------------------------------------------------------------------------------------------+",
"| CASE WHEN a.b IS NULL THEN NULL WHEN a.b < Int64(3) THEN NULL WHEN a.b >= Int64(3) THEN a.b + Int64(1) ELSE a.b END |",
"+---------------------------------------------------------------------------------------------------------------------+",
"| |",
"| |",
"| 4 |",
"+---------------------------------------------------------------------------------------------------------------------+",
];
assert_batches_eq!(expected, &actual);

let sql = "select case b when 1 then null when 2 then null when 3 then b + 1 else b end from (select a,b from (values (1,null),(1,2),(2,3)) as t (a,b)) a;";
let actual = execute_to_batches(&ctx, sql).await;

let expected = vec![
"+------------------------------------------------------------------------------------------------------------+",
"| CASE #a.b WHEN Int64(1) THEN NULL WHEN Int64(2) THEN NULL WHEN Int64(3) THEN #a.b + Int64(1) ELSE #a.b END |",
"+------------------------------------------------------------------------------------------------------------+",
"| |",
"| |",
"| 4 |",
"+------------------------------------------------------------------------------------------------------------+",
"+---------------------------------------------------------------------------------------------------------+",
"| CASE a.b WHEN Int64(1) THEN NULL WHEN Int64(2) THEN NULL WHEN Int64(3) THEN a.b + Int64(1) ELSE a.b END |",
"+---------------------------------------------------------------------------------------------------------+",
"| |",
"| |",
"| 4 |",
"+---------------------------------------------------------------------------------------------------------+",
];
assert_batches_eq!(expected, &actual);

Expand Down
14 changes: 7 additions & 7 deletions datafusion/core/tests/sql/projection.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -252,13 +252,13 @@ async fn project_cast_dictionary() {
let actual = collect(physical_plan, ctx.task_ctx()).await.unwrap();

let expected = vec![
"+------------------------------------------------------------------------------------+",
"| CASE WHEN #cpu_load_short.host IS NULL THEN Utf8(\"\") ELSE #cpu_load_short.host END |",
"+------------------------------------------------------------------------------------+",
"| host1 |",
"| |",
"| host2 |",
"+------------------------------------------------------------------------------------+",
"+----------------------------------------------------------------------------------+",
"| CASE WHEN cpu_load_short.host IS NULL THEN Utf8(\"\") ELSE cpu_load_short.host END |",
"+----------------------------------------------------------------------------------+",
"| host1 |",
"| |",
"| host2 |",
"+----------------------------------------------------------------------------------+",
];
assert_batches_eq!(expected, &actual);
}
Expand Down
66 changes: 66 additions & 0 deletions datafusion/optimizer/src/type_coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -354,6 +354,50 @@ impl ExprRewriter for TypeCoercionRewriter {
}
}
}
Expr::Case {
expr,
when_then_expr,
else_expr,
} => {
// all the result of then and else should be convert to a common data type,
// if they can be coercible to a common data type, return error.
let then_types = when_then_expr
.iter()
.map(|when_then| when_then.1.get_type(&self.schema))
.collect::<Result<Vec<_>>>()?;
let else_type = match &else_expr {
None => Ok(None),
Some(expr) => expr.get_type(&self.schema).map(Some),
}?;
let case_when_coerce_type =
get_coerce_type_for_case_when(&then_types, &else_type);
match case_when_coerce_type {
None => Err(DataFusionError::Internal(format!(
"Failed to coerce then ({:?}) and else ({:?}) to common types in CASE WHEN expression",
then_types, else_type
))),
Some(data_type) => {
let left = when_then_expr
.into_iter()
.map(|(when, then)| {
let then = then.cast_to(&data_type, &self.schema)?;
Ok((when, Box::new(then)))
})
.collect::<Result<Vec<_>>>()?;
let right = match else_expr {
None => None,
Some(expr) => {
Some(Box::new(expr.cast_to(&data_type, &self.schema)?))
}
};
Ok(Expr::Case {
expr,
when_then_expr: left,
else_expr: right,
})
}
}
}
expr => Ok(expr),
}
}
Expand Down Expand Up @@ -410,6 +454,28 @@ fn coerce_arguments_for_signature(
.collect::<Result<Vec<_>>>()
}

/// Find a common coerceable type for all `then_types` as well
/// and the `else_type`, if specified.
/// Returns the common data type for `then_types` and `else_type`
fn get_coerce_type_for_case_when(
then_types: &[DataType],
else_type: &Option<DataType>,
) -> Option<DataType> {
let else_type = match else_type {
None => then_types[0].clone(),
Some(data_type) => data_type.clone(),
};
then_types
.iter()
.fold(Some(else_type), |left, right_type| match left {
// failed to find a valid coercion in a previous iteration
None => None,
// TODO: now just use the `equal` coercion rule for case when. If find the issue, and
// refactor again.
Some(left_type) => comparison_coercion(&left_type, right_type),
})
}

#[cfg(test)]
mod test {
use crate::type_coercion::{TypeCoercion, TypeCoercionRewriter};
Expand Down
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