alamb commented on code in PR #20702:
URL: https://github.com/apache/datafusion/pull/20702#discussion_r2886623667
##########
datafusion/optimizer/src/simplify_expressions/regex.rs:
##########
@@ -39,7 +39,7 @@ const ANY_CHAR_REGEX_PATTERN: &str = ".*";
/// - partial anchored regex patterns (e.g. `^foo`) to `LIKE 'foo%'`
/// - combinations (alternatives) of the above, will be concatenated with `OR`
or `AND`
/// - `EQ .*` to NotNull
-/// - `NE .*` means IS EMPTY
+/// - `NE .*` to false (.* matches non-empty and empty strings, and NULL !~
'.*' results in NULL so this can never be true)
Review Comment:
I think it is only false in the context of filters (and this code can
currently be used for both filters and regular expressions)
I think `null !~ '.*'` is actually `null` (not `false`)
I think a correct rewrite is
```sql
CASE
WHEN col IS NOT NULL THEN FALSE
ELSE NULL
END
```
##########
datafusion/optimizer/src/simplify_expressions/simplify_exprs.rs:
##########
@@ -883,17 +883,17 @@ mod tests {
"
)?;
- // Test `!= ".*"` transforms to checking if the column is empty
+ // Test `!~ ".*"` transforms to false
Review Comment:
can we please also add a test explicitly for a null input?
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