SQL data sources: Convert to return data frames (#32257)

Convert SQL data sources to return data frames.

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>
Co-authored-by: Will Browne <will.browne@grafana.com>
Co-authored-by: Hugo Häggmark <hugo.haggmark@gmail.com>

pkg/tsdb/sqleng/resample.go

@@ -0,0 +1,136 @@
+package sqleng
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+)
+
+// getRowFillValues populates a slice of values corresponding to the provided data.Frame fields.
+// Uses data.FillMissing settings to fill in values that are missing. Values are normally missing
+// due to that the selected query interval doesn't match the intervals of the data returned from
+// the query and therefore needs to be resampled.
+func getRowFillValues(f *data.Frame, tsSchema data.TimeSeriesSchema, currentTime time.Time,
+	fillMissing *data.FillMissing, intermediateRows []int, lastSeenRowIdx int) []interface{} {
+	vals := make([]interface{}, 0, len(f.Fields))
+	for i, field := range f.Fields {
+		// if the current field is the time index of the series
+		// set the new value to be added to the new timestamp
+		if i == tsSchema.TimeIndex {
+			switch f.Fields[tsSchema.TimeIndex].Type() {
+			case data.FieldTypeTime:
+				vals = append(vals, currentTime)
+			default:
+				vals = append(vals, &currentTime)
+			}
+			continue
+		}
+
+		isValueField := false
+		for _, idx := range tsSchema.ValueIndices {
+			if i == idx {
+				isValueField = true
+				break
+			}
+		}
+
+		// if the current field is value Field
+		// set the new value to the last seen field value (if such exists)
+		// otherwise set the appropriate value according to the fillMissing mode
+		// if the current field is string field)
+		// set the new value to be added to the last seen value (if such exists)
+		// if the Frame is wide then there should not be any string fields
+		var newVal interface{}
+		if isValueField {
+			if len(intermediateRows) > 0 {
+				// instead of setting the last seen
+				// we could set avg, sum, min or max
+				// of the intermediate values for each field
+				newVal = f.At(i, intermediateRows[len(intermediateRows)-1])
+			} else {
+				val, err := data.GetMissing(fillMissing, field, lastSeenRowIdx)
+				if err == nil {
+					newVal = val
+				}
+			}
+		} else if lastSeenRowIdx >= 0 {
+			newVal = f.At(i, lastSeenRowIdx)
+		}
+		vals = append(vals, newVal)
+	}
+	return vals
+}
+
+// resample resample provided time-series data.Frame.
+// This is needed in the case of the selected query interval doesn't
+// match the intervals of the time-series field in the data.Frame and
+// therefore needs to be resampled.
+func resample(f *data.Frame, qm dataQueryModel) (*data.Frame, error) {
+	tsSchema := f.TimeSeriesSchema()
+	if tsSchema.Type == data.TimeSeriesTypeNot {
+		return f, fmt.Errorf("can not fill missing, not timeseries frame")
+	}
+
+	if qm.Interval == 0 {
+		return f, nil
+	}
+
+	newFields := make([]*data.Field, 0, len(f.Fields))
+	for _, field := range f.Fields {
+		newField := data.NewFieldFromFieldType(field.Type(), 0)
+		newField.Name = field.Name
+		newField.Labels = field.Labels
+		newFields = append(newFields, newField)
+	}
+	resampledFrame := data.NewFrame(f.Name, newFields...)
+	resampledFrame.Meta = f.Meta
+
+	resampledRowidx := 0
+	lastSeenRowIdx := -1
+	timeField := f.Fields[tsSchema.TimeIndex]
+
+	for currentTime := qm.TimeRange.From; !currentTime.After(qm.TimeRange.To); currentTime = currentTime.Add(qm.Interval) {
+		initialRowIdx := 0
+		if lastSeenRowIdx > 0 {
+			initialRowIdx = lastSeenRowIdx + 1
+		}
+		intermediateRows := make([]int, 0)
+		for {
+			rowLen, err := f.RowLen()
+			if err != nil {
+				return f, err
+			}
+			if initialRowIdx == rowLen {
+				break
+			}
+
+			t, ok := timeField.ConcreteAt(initialRowIdx)
+			if !ok {
+				return f, fmt.Errorf("time point is nil")
+			}
+
+			if t.(time.Time).After(currentTime) {
+				nextTime := currentTime.Add(qm.Interval)
+				if t.(time.Time).Before(nextTime) {
+					intermediateRows = append(intermediateRows, initialRowIdx)
+					lastSeenRowIdx = initialRowIdx
+					initialRowIdx++
+				}
+				break
+			}
+
+			intermediateRows = append(intermediateRows, initialRowIdx)
+			lastSeenRowIdx = initialRowIdx
+			initialRowIdx++
+		}
+
+		// no intermediate points; set values following fill missing mode
+		fieldVals := getRowFillValues(f, tsSchema, currentTime, qm.FillMissing, intermediateRows, lastSeenRowIdx)
+
+		resampledFrame.InsertRow(resampledRowidx, fieldVals...)
+		resampledRowidx++
+	}
+
+	return resampledFrame, nil
+}