kosiew commented on code in PR #22564:
URL: https://github.com/apache/datafusion/pull/22564#discussion_r3338184839


##########
datafusion/functions/src/math/log.rs:
##########
@@ -358,43 +386,83 @@ impl ScalarUDFImpl for LogFunc {
         } else {
             lit(ScalarValue::new_ten(&number_datatype)?)
         };
+        let base_datatype = info.get_data_type(&base)?;
+
+        if is_zero_literal(&number, &number_datatype)?
+            || is_zero_literal(&base, &base_datatype)?
+        {
+            return Ok(ExprSimplifyResult::Original(original_log_args(
+                num_args, &base, &number,
+            )?));
+        }
+
+        let base_is_valid_literal = is_valid_log_base_literal(&base)?;
 
         match number {
             Expr::Literal(value, _)
-                if value == ScalarValue::new_one(&number_datatype)? =>
+                if value == ScalarValue::new_one(&number_datatype)?
+                    && base_is_valid_literal =>
             {
                 Ok(ExprSimplifyResult::Simplified(lit(ScalarValue::new_zero(
                     &info.get_data_type(&base)?,
                 )?)))
             }
             Expr::ScalarFunction(ScalarFunction { func, mut args })
-                if is_pow(&func) && args.len() == 2 && base == args[0] =>
+                if is_pow(&func)
+                    && args.len() == 2
+                    && base == args[0]
+                    && base_is_valid_literal =>

Review Comment:
   I think we should temporarily abandon these reverse-op simplifications. We 
do not know
    │ the true runtime range of columns or arbitrary expressions, and the 
rewrite can
    │ remove validation that should happen at execution time. Safer to only 
simplify
    │ literal/fully constant cases, or skip the rewrite unless non-zero can be 
proven.
   



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