jonahgao commented on code in PR #9790:
URL: https://github.com/apache/arrow-datafusion/pull/9790#discussion_r1539358701
##########
datafusion/sql/src/query.rs:
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@@ -283,3 +276,44 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
}
}
}
+
+/// Retrieves the constant result of an expression, evaluating it if possible.
+///
+/// This function takes an expression and an argument name as input and returns
+/// a `Result<i64>` indicating either the constant result of the expression or
an
+/// error if the expression cannot be evaluated.
+///
+/// # Arguments
+///
+/// * `expr` - An `Expr` representing the expression to evaluate.
+/// * `arg_name` - The name of the argument for error messages.
+///
+/// # Returns
+///
+/// * `Result<i64>` - An `Ok` variant containing the constant result if
evaluation is successful,
+/// or an `Err` variant containing an error message if evaluation fails.
+fn get_constant_result(expr: &Expr, arg_name: &str) -> Result<i64> {
+ match expr {
Review Comment:
Could we change the `Limit` logical plan to support arbitrary expressions?
```rust
pub struct Limit {
pub skip: Expr,
pub fetch: Option<Expr>,
pub input: Arc<LogicalPlan>,
}
```
The `SimplifyExpressions` rule can automatically optimize them into
constants. Some optimization rules such as `PushDownLimit` only run when the
limit expression is a constant. We may need to add a cast for the limit
expression when planning, only checking if it is a constant of type u64.
When creating the `LimitExec` physical plan, convert the limit expression
into `PhysicalExpr` and evaluate it.
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