SQL Expressions: Make SQL Expressions work with Alerting (#101820)

Initial support for alerting with SQL expressions

- When `format` is set to `alerting`, SQL expressions output in a format suitable for alerting evaluation.
- Outstanding TODOs:
  - Deduplicate output rows
  - Add more tests
  - Fix broken alerting UI rendering (likely due to shape change to undocumented full-long format)
- Basic usage:
  - SQL must return one numeric column and one or more string columns.
  - Each row may become an alert.
  - The alert fires if the numeric value is non-zero.
  - String columns are treated as labels.

---------

Co-authored-by: Konrad Lalik <konradlalik@gmail.com>
Co-authored-by: Tom Ratcliffe <tom.ratcliffe@grafana.com>
Co-authored-by: Sam Jewell <sam.jewell@grafana.com>

pkg/expr/sql_command_alert_test.go

@@ -0,0 +1,80 @@
+package expr
+
+import (
+	"testing"
+
+	"github.com/grafana/grafana-plugin-sdk-go/data"
+	"github.com/stretchr/testify/require"
+)
+
+func TestExtractNumberSetFromSQLForAlerting(t *testing.T) {
+	t.Run("SingleRowNoLabels", func(t *testing.T) {
+		input := data.NewFrame("",
+			data.NewField(SQLMetricFieldName, nil, []string{"cpu"}), // will be treated as a label
+			data.NewField(SQLValueFieldName, nil, []*float64{fp(3.14)}),
+		)
+
+		numbers, err := extractNumberSetFromSQLForAlerting(input)
+		require.NoError(t, err)
+		require.Len(t, numbers, 1)
+
+		got := numbers[0]
+		require.Equal(t, fp(3.14), got.GetFloat64Value())
+		require.Equal(t, data.Labels{
+			SQLMetricFieldName: "cpu",
+		}, got.GetLabels())
+	})
+
+	t.Run("TwoRowsWithLabelsAndDisplay", func(t *testing.T) {
+		input := data.NewFrame("",
+			data.NewField(SQLMetricFieldName, nil, []string{"cpu", "cpu"}),
+			data.NewField(SQLValueFieldName, nil, []*float64{fp(1.0), fp(2.0)}),
+			data.NewField(SQLDisplayFieldName, nil, []*string{sp("CPU A"), sp("CPU A")}),
+			data.NewField("host", nil, []*string{sp("a"), sp("a")}),
+		)
+
+		numbers, err := extractNumberSetFromSQLForAlerting(input)
+		require.NoError(t, err)
+		require.Len(t, numbers, 2)
+
+		require.Equal(t, fp(1.0), numbers[0].GetFloat64Value())
+		require.Equal(t, data.Labels{
+			SQLMetricFieldName:  "cpu",
+			SQLDisplayFieldName: "CPU A",
+			"host":              "a",
+		}, numbers[0].GetLabels())
+
+		require.Equal(t, fp(2.0), numbers[1].GetFloat64Value())
+		require.Equal(t, data.Labels{
+			SQLMetricFieldName:  "cpu",
+			SQLDisplayFieldName: "CPU A",
+			"host":              "a",
+		}, numbers[1].GetLabels())
+	})
+
+	t.Run("TwoFieldsWithSparseLabels", func(t *testing.T) {
+		input := data.NewFrame("",
+			data.NewField(SQLMetricFieldName, nil, []string{"cpu", "cpu"}),
+			data.NewField(SQLValueFieldName, nil, []*float64{fp(1.0), fp(2.0)}),
+			data.NewField("env", nil, []*string{nil, sp("prod")}),
+			data.NewField("host", nil, []*string{sp("a"), sp("b")}),
+		)
+
+		numbers, err := extractNumberSetFromSQLForAlerting(input)
+		require.NoError(t, err)
+		require.Len(t, numbers, 2)
+
+		require.Equal(t, fp(1.0), numbers[0].GetFloat64Value())
+		require.Equal(t, data.Labels{
+			SQLMetricFieldName: "cpu",
+			"host":             "a",
+		}, numbers[0].GetLabels())
+
+		require.Equal(t, fp(2.0), numbers[1].GetFloat64Value())
+		require.Equal(t, data.Labels{
+			SQLMetricFieldName: "cpu",
+			"host":             "b",
+			"env":              "prod",
+		}, numbers[1].GetLabels())
+	})
+}