[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #2694: Combine limit and offset to `fetch` and `skip` and implement physical plan support

[GitBox <gi...@apache.org>]

alamb commented on code in PR #2694:
URL: https://github.com/apache/arrow-datafusion/pull/2694#discussion_r892792342


##########
datafusion/sql/src/planner.rs:
##########
@@ -1212,57 +1206,59 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
     }
 
     /// Wrap a plan in a limit
-    fn limit(&self, input: LogicalPlan, limit: Option<SQLExpr>) -> Result<LogicalPlan> {
-        match limit {
-            Some(limit_expr) => {
-                let n = match self.sql_to_rex(
-                    limit_expr,
-                    input.schema(),
-                    &mut HashMap::new(),
-                )? {
-                    Expr::Literal(ScalarValue::Int64(Some(n))) => Ok(n as usize),
-                    _ => Err(DataFusionError::Plan(
-                        "Unexpected expression for LIMIT clause".to_string(),
-                    )),
-                }?;
-
-                LogicalPlanBuilder::from(input).limit(n)?.build()
-            }
-            _ => Ok(input),
-        }
-    }
-
-    /// Wrap a plan in a offset
-    fn offset(
+    fn limit(
         &self,
         input: LogicalPlan,
-        offset: Option<SQLOffset>,
+        skip: Option<SQLOffset>,
+        fetch: Option<SQLExpr>,
     ) -> Result<LogicalPlan> {
-        match offset {
-            Some(offset_expr) => {
-                let offset = match self.sql_to_rex(
-                    offset_expr.value,
+        if skip.is_none() && fetch.is_none() {
+            return Ok(input);
+        }
+
+        let skip = match skip {

Review Comment:
   This compiled for me:
   
   ```rust
   
           let skip = skip
               .map(|skip_expr| {
                   let skip = match self.sql_to_rex(
                       skip_expr.value,
                       input.schema(),
                       &mut HashMap::new(),
                   )? {
                       Expr::Literal(ScalarValue::Int64(Some(s))) => {
                           if s < 0 {
                               return Err(DataFusionError::Plan(format!(
                                   "Offset must be >= 0, '{}' was provided.",
                                   s
                               )));
                           }
                           Ok(s as usize)
                       }
                       _ => Err(DataFusionError::Plan(
                           "Unexpected expression in OFFSET clause".to_string(),
                       )),
                   }?;
                   Ok(skip)
               })
               .transpose()?;
   
   ```
   
   But I don't think it is all that much more readable than what you have in this PR



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