findepi commented on PR #16745:
URL: https://github.com/apache/datafusion/pull/16745#issuecomment-3108936064
You're absolutely right. The ORDER BY ordering and `<` operator are not the
same thing.
The ORDER BY places NaN as higher than +inf, while `<` operator _should
likely_ return false for any `<` comparison involving NaN (same for `=`).
> However, SQL comparisons follow IEEE 754 ordering semantics, so -0.0 ==
0.0 is true, and both -0.0 < 0.0 and -0.0 > 0.0 are false.
Not sure whether you mean SQL spec, or what's implemented in DataFusion, or
what DataFusion should be implementing?
What's currently implemented seems to be this:
```
> WITH fs AS (SELECT t::float AS f FROM (values ('0'), ('-0'), ('NaN')) _(t))
SELECT f1, f2, f1 = f2, f1 < f2, f2 < f1
FROM fs _(f1), fs _(f2);
+------+------+-------------+-------------+-------------+
| f1 | f2 | _.f1 = _.f2 | _.f1 < _.f2 | _.f2 < _.f1 |
+------+------+-------------+-------------+-------------+
| 0.0 | 0.0 | true | false | false |
| 0.0 | -0.0 | false | false | true | -- apparently 0
compares greater than -0
| 0.0 | NaN | false | true | false | -- apparently 0
compares less than NaN
| -0.0 | 0.0 | false | true | false | -- apparently -0
compares less than 0
| -0.0 | -0.0 | true | false | false |
| -0.0 | NaN | false | true | false |
| NaN | 0.0 | false | false | true |
| NaN | -0.0 | false | false | true |
| NaN | NaN | true | false | false | -- Is NaN = NaN
following IEEE 754? at least in C it's false
+------+------+-------------+-------------+-------------+
9 row(s) fetched.
Elapsed 0.016 seconds.
```
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