From 9902a56132fd7aa264a82229de2ce5188fcca08a Mon Sep 17 00:00:00 2001
From: Daito Akimura <>
Date: Thu, 14 Nov 2019 10:31:53 +0900
Subject: [PATCH] select columns feature

---
 frontend/query.go        | 12 +++++++++++-
 utils/io/columnseries.go | 21 +++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/frontend/query.go b/frontend/query.go
index 8b55c46a6..3ecd89020 100644
--- a/frontend/query.go
+++ b/frontend/query.go
@@ -34,6 +34,8 @@ type QueryRequest struct {
 	LimitRecordCount *int `msgpack:"limit_record_count,omitempty"`
 	// Set to true if LimitRecordCount should be from the lower
 	LimitFromStart *bool `msgpack:"limit_from_start,omitempty"`
+	// Array of column names to be returned
+	Columns []string `msgpack:"columns,omitempty"`
 
 	// Support for functions is experimental and subject to change
 	Functions []string `msgpack:"functions,omitempty"`
@@ -162,6 +164,10 @@ func (s *DataService) Query(r *http.Request, reqs *MultiQueryRequest, response *
 			if req.LimitFromStart != nil {
 				limitFromStart = *req.LimitFromStart
 			}
+			columns := make([]string, 0)
+			if req.Columns != nil {
+				columns = req.Columns
+			}
 
 			start := io.ToSystemTimezone(time.Unix(epochStart, 0))
 			stop := io.ToSystemTimezone(time.Unix(epochEnd, 0))
@@ -169,6 +175,7 @@ func (s *DataService) Query(r *http.Request, reqs *MultiQueryRequest, response *
 				dest,
 				start, stop,
 				limitRecordCount, limitFromStart,
+				columns,
 			)
 			if err != nil {
 				return err
@@ -241,7 +248,7 @@ Utility functions
 */
 
 func executeQuery(tbk *io.TimeBucketKey, start, end time.Time, LimitRecordCount int,
-	LimitFromStart bool) (io.ColumnSeriesMap, error) {
+	LimitFromStart bool, columns []string) (io.ColumnSeriesMap, error) {
 
 	query := planner.NewQuery(executor.ThisInstance.CatalogDir)
 
@@ -291,6 +298,9 @@ func executeQuery(tbk *io.TimeBucketKey, start, end time.Time, LimitRecordCount
 		log.Error("Error returned from query scanner: %s\n", err)
 		return nil, err
 	}
+
+	csm.FilterColumns(columns)
+
 	return csm, err
 }
 
diff --git a/utils/io/columnseries.go b/utils/io/columnseries.go
index 550f46c98..1dec89dc3 100644
--- a/utils/io/columnseries.go
+++ b/utils/io/columnseries.go
@@ -2,6 +2,7 @@ package io
 
 import (
 	"fmt"
+	"github.com/alpacahq/marketstore/utils/log"
 	"reflect"
 	"sort"
 	"strconv"
@@ -423,6 +424,26 @@ func (csm ColumnSeriesMap) ToRowSeriesMap(dataShapesMap map[TimeBucketKey][]Data
 	return rsMap
 }
 
+// FilterColumns removes columns other than the specified columns from all ColumnSeries in a ColumnSeriesMap.
+func (csm *ColumnSeriesMap) FilterColumns(columns []string) {
+	if len(columns) == 0 {
+		return
+	}
+
+	// index columns (=Epoch and Nanoseconds) are always necessary and Epoch should be the first column
+	keepColumns := []string{"Epoch"}
+	keepColumns = append(keepColumns, columns...)
+	keepColumns = append(keepColumns, "Nanoseconds")
+
+	for _, cs := range *csm {
+		// filter out unnecessary columns
+		err := cs.Project(keepColumns)
+		if err != nil {
+			log.Error("failed to filter out columns", keepColumns)
+		}
+	}
+}
+
 func GetNamesFromDSV(dataShapes []DataShape) (out []string) {
 	for _, shape := range dataShapes {
 		out = append(out, shape.Name)