refactor: use struct-style selectors in InfluxRPC (#7742)

Some clean up before I implement the core logic for #7533.

iox_query_influxrpc/src/lib.rs

@@ -5,8 +5,11 @@ use data_types::ChunkId;
 use datafusion::{
     common::DFSchemaRef,
     error::DataFusionError,
-    logical_expr::{utils::exprlist_to_columns, ExprSchemable, LogicalPlan, LogicalPlanBuilder},
+    logical_expr::{
+        utils::exprlist_to_columns, ExprSchemable, GetIndexedField, LogicalPlan, LogicalPlanBuilder,
+    },
     prelude::{when, Column, Expr},
+    scalar::ScalarValue,
 };
 use datafusion_util::AsExpr;
 use futures::{Stream, StreamExt, TryStreamExt};
@@ -35,7 +38,9 @@ use predicate::{
 use query_functions::{
     group_by::{Aggregate, WindowDuration},
     make_window_bound_expr,
-    selectors::{selector_first, selector_last, selector_max, selector_min, SelectorOutput},
+    selectors::{
+        struct_selector_first, struct_selector_last, struct_selector_max, struct_selector_min,
+    },
 };
 use schema::{InfluxColumnType, Projection, Schema, TIME_COLUMN_NAME};
 use snafu::{ensure, OptionExt, ResultExt, Snafu};
@@ -1636,7 +1641,6 @@ pub(crate) struct AggExprs {
 struct FieldExpr<'a> {
     expr: Expr,
     name: &'a str,
-    datatype: &'a DataType,
 }
 
 // Returns an iterator of fields from schema that pass the predicate. If there
@@ -1674,7 +1678,6 @@ fn filtered_fields_iter<'a>(
         Some(FieldExpr {
             expr: expr.alias(f.name()),
             name: f.name(),
-            datatype: f.data_type(),
         })
     })
 }
@@ -1735,22 +1738,25 @@ impl AggExprs {
         let mut field_list = Vec::new();
 
         for field in filtered_fields_iter(schema, predicate) {
+            let selector = make_selector_expr(agg, field.clone())?;
+
             let field_name = field.name;
-            agg_exprs.push(make_selector_expr(
-                agg,
-                SelectorOutput::Value,
-                field.clone(),
-                field_name,
-            )?);
+            agg_exprs.push(
+                Expr::GetIndexedField(GetIndexedField {
+                    expr: Box::new(selector.clone()),
+                    key: ScalarValue::from("value"),
+                })
+                .alias(field_name),
+            );
 
             let time_column_name = format!("{TIME_COLUMN_NAME}_{field_name}");
-
-            agg_exprs.push(make_selector_expr(
-                agg,
-                SelectorOutput::Time,
-                field,
-                &time_column_name,
-            )?);
+            agg_exprs.push(
+                Expr::GetIndexedField(GetIndexedField {
+                    expr: Box::new(selector.clone()),
+                    key: ScalarValue::from("time"),
+                })
+                .alias(&time_column_name),
+            );
 
             field_list.push((
                 Arc::from(field_name), // value name
@@ -1782,7 +1788,6 @@ impl AggExprs {
                     agg,
                     FieldExpr {
                         expr: field.name().as_expr(),
-                        datatype: field.data_type(),
                         name: field.name(),
                     },
                 )
@@ -1866,23 +1871,16 @@ fn make_agg_expr(agg: Aggregate, field_expr: FieldExpr<'_>) -> Result<Expr> {
 ///     ELSE NULL
 /// END) as col_name
 ///
-fn make_selector_expr<'a>(
-    agg: Aggregate,
-    output: SelectorOutput,
-    field: FieldExpr<'a>,
-    col_name: &'a str,
-) -> Result<Expr> {
+fn make_selector_expr(agg: Aggregate, field: FieldExpr<'_>) -> Result<Expr> {
     let uda = match agg {
-        Aggregate::First => selector_first(field.datatype, output),
-        Aggregate::Last => selector_last(field.datatype, output),
-        Aggregate::Min => selector_min(field.datatype, output),
-        Aggregate::Max => selector_max(field.datatype, output),
+        Aggregate::First => struct_selector_first(),
+        Aggregate::Last => struct_selector_last(),
+        Aggregate::Min => struct_selector_min(),
+        Aggregate::Max => struct_selector_max(),
         _ => return InternalAggregateNotSelectorSnafu { agg }.fail(),
     };
 
-    Ok(uda
-        .call(vec![field.expr, TIME_COLUMN_NAME.as_expr()])
-        .alias(col_name))
+    Ok(uda.call(vec![field.expr, TIME_COLUMN_NAME.as_expr()]))
 }
 
 /// Orders chunks so it is likely that the ones that already have cached data are pulled first.