pepijnve commented on code in PR #17813:
URL: https://github.com/apache/datafusion/pull/17813#discussion_r2388499076
##########
datafusion/expr/src/expr_schema.rs:
##########
@@ -830,6 +883,150 @@ mod tests {
assert!(expr.nullable(&get_schema(false)).unwrap());
}
+ fn check_nullability(
+ expr: Expr,
+ nullable: bool,
+ get_schema: fn(bool) -> MockExprSchema,
+ ) -> Result<()> {
+ assert_eq!(
+ expr.nullable(&get_schema(true))?,
+ nullable,
+ "Nullability of '{expr}' should be {nullable} when column is
nullable"
+ );
+ assert!(
+ !expr.nullable(&get_schema(false))?,
+ "Nullability of '{expr}' should be false when column is not
nullable"
+ );
+ Ok(())
+ }
+
+ #[test]
+ fn test_case_expression_nullability() -> Result<()> {
+ let get_schema = |nullable| {
+ MockExprSchema::new()
+ .with_data_type(DataType::Int32)
+ .with_nullable(nullable)
+ };
+
+ check_nullability(
+ when(is_not_null(col("foo")), col("foo")).otherwise(lit(0))?,
+ false,
+ get_schema,
+ )?;
+
+ check_nullability(
+ when(not(is_null(col("foo"))), col("foo")).otherwise(lit(0))?,
+ false,
+ get_schema,
+ )?;
+
+ check_nullability(
+ when(binary_expr(col("foo"), Operator::Eq, lit(5)), col("foo"))
+ .otherwise(lit(0))?,
+ true,
Review Comment:
Agreed, the const evaluation is far from complete. I tried to do something
good enough for the coalesce simplification initially.
I was wondering the whole time if there isn't some existing null analysis
logic somewhere in the codebase we could reuse. The best I could come up with
is rewriting the full expression by replacing the `then` expression with
literal `NULL` and then attempting const evaluation. But that got me worrying
about planning overhead again.
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