kczimm commented on code in PR #15980:
URL: https://github.com/apache/datafusion/pull/15980#discussion_r2080118522


##########
datafusion/expr/src/logical_plan/plan.rs:
##########
@@ -1494,6 +1494,14 @@ impl LogicalPlan {
         let mut param_types: HashMap<String, Option<DataType>> = 
HashMap::new();
 
         self.apply_with_subqueries(|plan| {
+            if let LogicalPlan::Limit(Limit { fetch: Some(e), .. }) = plan {

Review Comment:
   My test is actually really unfair, I will modify it. I constructed 
`LogicalPlan` by hand and gave it no opportunity to do any placeholder type 
inference.
   
   `Expr::infer_placeholder_types` takes an `Expr` and a `DFSchema` and it uses 
the schema to infer the datatype from the field type. However, there is no 
schema that will provide that information for `LIMIT`. It's a special case and 
we (I believe) always know what datatype it must be and it need not be 
inferred. I think the case is the same for `offset` as you mention. In fact, it 
looks like we try to coerce it to be Int64, 
https://github.com/apache/datafusion/blob/41e7aed3a943134c40d1b18cb9d424b358b5e5b1/datafusion/optimizer/src/analyzer/type_coercion.rs#L242.



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