diff --git a/sql/src/influxql/planner.rs b/sql/src/influxql/planner.rs
index 0c8496a21e..bdefa32cbc 100644
--- a/sql/src/influxql/planner.rs
+++ b/sql/src/influxql/planner.rs
@@ -9,9 +9,8 @@ use influxql_logical_planner::planner::InfluxQLToLogicalPlan;
 use influxql_parser::statement::Statement as InfluxqlStatement;
 use snafu::ResultExt;
 
-use super::provider::InfluxSchemaProviderImpl;
 use crate::{
-    influxql::error::*,
+    influxql::{error::*, provider::InfluxSchemaProviderImpl},
     plan::{Plan, QueryPlan},
     provider::{ContextProviderAdapter, MetaProvider},
 };
diff --git a/sql/src/influxql/provider.rs b/sql/src/influxql/provider.rs
index 7694b26c1b..8a19eb1f41 100644
--- a/sql/src/influxql/provider.rs
+++ b/sql/src/influxql/provider.rs
@@ -125,14 +125,17 @@ fn map_column_to_influx_column(
     is_timestamp_key: bool,
 ) -> Result<InfluxColumnType> {
     if is_timestamp_key {
-        map_column_to_influx_time_column(column)
-    } else if column.is_tag {
-        map_column_to_influx_tag_column(column)
-    } else {
-        map_column_to_influx_field_column(column)
+        return map_column_to_influx_time_column(column);
+    }
+
+    if column.is_tag {
+        return map_column_to_influx_tag_column(column);
     }
+
+    map_column_to_influx_field_column(column)
 }
 
+// TODO: don't restrict the time column name.
 fn map_column_to_influx_time_column(column: &ColumnSchema) -> Result<InfluxColumnType> {
     if column.name == "time" && !column.is_nullable {
         Ok(InfluxColumnType::Timestamp)
@@ -144,8 +147,8 @@ fn map_column_to_influx_time_column(column: &ColumnSchema) -> Result<InfluxColum
     }
 }
 
+// TODO: support more tag types.
 fn map_column_to_influx_tag_column(column: &ColumnSchema) -> Result<InfluxColumnType> {
-    // Tag column
     if matches!(column.data_type, DatumKind::String) && column.is_nullable {
         Ok(InfluxColumnType::Tag)
     } else {
@@ -156,6 +159,7 @@ fn map_column_to_influx_tag_column(column: &ColumnSchema) -> Result<InfluxColumn
     }
 }
 
+// TODO: support more field types.
 fn map_column_to_influx_field_column(column: &ColumnSchema) -> Result<InfluxColumnType> {
     if column.is_nullable {
         match column.data_type {
diff --git a/sql/src/planner.rs b/sql/src/planner.rs
index 47aabef7b9..896b43b25d 100644
--- a/sql/src/planner.rs
+++ b/sql/src/planner.rs
@@ -331,7 +331,6 @@ impl<'a, P: MetaProvider> Planner<'a, P> {
 
     pub fn influxql_stmt_to_plan(&self, statement: InfluxqlStatement) -> Result<Plan> {
         let adapter = ContextProviderAdapter::new(self.provider, self.read_parallelism);
-        // let planner = PlannerDelegate::new(adapter);
 
         let influxql_planner = crate::influxql::planner::Planner::new(adapter);
         influxql_planner