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signum function incompatible with Postgres and Apache Spark #11557
Description
Describe the bug
In Postgres and Apache Spark, signum returns -1 for negative integers, 0 for zero, and 1 for positive integers.
DataFusion uses Rust's signum function, which has different behavior.
❯ select signum(-1), signum(0), signum(1);
+-------------------+------------------+------------------+
| signum(Int64(-1)) | signum(Int64(0)) | signum(Int64(1)) |
+-------------------+------------------+------------------+
| -1.0 | 1.0 | 1.0 |
+-------------------+------------------+------------------+
For floating-point inputs, Apache Spark returns -1 for -0.0 and 1 for +0.0. I have not researched what Postgres does in this case.
Activity
goldmedal commentedon Jul 20, 2024
take
goldmedal commentedon Jul 20, 2024
I will solve another issue first. I'll take it back if no one else works on it after I finish.
getChan commentedon Jul 20, 2024
take
getChan commentedon Jul 21, 2024
Comparison of the signum function between DataFusion SQL and Rust
-1_i32)0_i32)1_i32)-0.0_f32)0.0_f32)In Rust, the definition of the signum function for floating point types is as follows:
My guess is that the implementation of the signum function in DataFusion only accepts floating point types as input. Consequently, if it receives 0 as input, it appears to convert it to Rust’s 0.0 and output
1ref) https://github.com/apache/datafusion/blob/main/datafusion/functions/src/macros.rs#L225-L254
implementation
If you have any other opinions, please let me know.
docs: fix signum documentation to say zero returns 0 (apache#24324)
docs: fix signum documentation to say zero returns 0 (apache#24324)