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Simplify IsNotNull and IsNull expression #6345

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Merged
merged 1 commit into from
May 15, 2023
Merged

Simplify IsNotNull and IsNull expression #6345

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34 changes: 34 additions & 0 deletions datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1161,6 +1161,12 @@ impl<'a, S: SimplifyInfo> TreeNodeRewriter for Simplifier<'a, S> {
lit(!negated)
}

// a IS NOT NULL --> true, if a is not nullable
Expr::IsNotNull(expr) if !info.nullable(&expr)? => lit(true),
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@comphead comphead May 12, 2023

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Thanks @byteink. would you mind adding more description? Why the simplification needed and what exactly problem it solves? is it a bug or something?

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@jackwener jackwener May 13, 2023 •
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create table test(a int not null);

select a is null

we can convert it into

select false

because a is not null

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@jonahgao jonahgao May 13, 2023

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@comphead It is not a bug. I've added some descriptions.


// a IS NULL --> false, if a is not nullable
Expr::IsNull(expr) if !info.nullable(&expr)? => lit(false),

// no additional rewrites possible
expr => expr,
};
Expand Down Expand Up @@ -2596,6 +2602,34 @@ mod tests {
);
}

#[test]
fn simplify_expr_is_not_null() {
assert_eq!(
simplify(Expr::IsNotNull(Box::new(col("c1")))),
Expr::IsNotNull(Box::new(col("c1")))
);

// 'c1_non_null IS NOT NULL' is always true
assert_eq!(
simplify(Expr::IsNotNull(Box::new(col("c1_non_null")))),
lit(true)
);
}

#[test]
fn simplify_expr_is_null() {
assert_eq!(
simplify(Expr::IsNull(Box::new(col("c1")))),
Expr::IsNull(Box::new(col("c1")))
);

// 'c1_non_null IS NULL' is always false
assert_eq!(
simplify(Expr::IsNull(Box::new(col("c1_non_null")))),
lit(false)
);
}

#[test]
fn simplify_expr_eq() {
let schema = expr_test_schema();
Expand Down
35 changes: 31 additions & 4 deletions datafusion/optimizer/src/simplify_expressions/simplify_exprs.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -167,6 +167,7 @@ mod tests {
Field::new("b", DataType::Boolean, false),
Field::new("c", DataType::Boolean, false),
Field::new("d", DataType::UInt32, false),
Field::new("e", DataType::UInt32, true),
]);
table_scan(Some("test"), &schema, None)
.expect("creating scan")
Expand Down Expand Up @@ -623,9 +624,9 @@ mod tests {
let table_scan = test_table_scan();

let plan = LogicalPlanBuilder::from(table_scan)
.filter(col("d").is_null().not())?
.filter(col("e").is_null().not())?
.build()?;
let expected = "Filter: test.d IS NOT NULL\
let expected = "Filter: test.e IS NOT NULL\
\n TableScan: test";

assert_optimized_plan_eq(&plan, expected)
Expand All @@ -636,9 +637,9 @@ mod tests {
let table_scan = test_table_scan();

let plan = LogicalPlanBuilder::from(table_scan)
.filter(col("d").is_not_null().not())?
.filter(col("e").is_not_null().not())?
.build()?;
let expected = "Filter: test.d IS NULL\
let expected = "Filter: test.e IS NULL\
\n TableScan: test";

assert_optimized_plan_eq(&plan, expected)
Expand Down Expand Up @@ -848,4 +849,30 @@ mod tests {
"TableScan: test, unsupported_filters=[g = f AS g = power(f,Float64(1))]";
assert_optimized_plan_eq(&plan, expected)
}

#[test]
fn simplify_is_not_null() -> Result<()> {
let table_scan = test_table_scan();

let plan = LogicalPlanBuilder::from(table_scan)
.filter(col("d").is_not_null())?
.build()?;
let expected = "Filter: Boolean(true)\
\n TableScan: test";

assert_optimized_plan_eq(&plan, expected)
}

#[test]
fn simplify_is_null() -> Result<()> {
let table_scan = test_table_scan();

let plan = LogicalPlanBuilder::from(table_scan)
.filter(col("d").is_null())?
.build()?;
let expected = "Filter: Boolean(false)\
\n TableScan: test";

assert_optimized_plan_eq(&plan, expected)
}
}