Use parenthesis to surround the selected tags for influxdb queries (#9131)

The generated queries when selecting multiple tags are incorrect. In
InfluxQL, `AND` has a higher precedence than `OR` so the condition:

    WHERE "hostname" = 'server1' OR "hostname" = 'server2' AND time > now() - 5m

This is parsed as if it were:

    WHERE "hostname" = 'server1' OR ("hostname" = 'server2' AND time > now() - 5m)

But the intention is to write a query like this:

    WHERE ("hostname" = 'server1' OR "hostname" = 'server2') AND time > now() - 5m

This change modifies the generated query so it surrounds a query with
multiple conditions in parenthesis so it doesn't conflict with the time
expression in an unexpected way.

This is currently not an issue because InfluxDB doesn't actually
evaluate the condition for the time expression correctly. It just looks
through the AST for anything that looks like a time expression and then
assumes the proper format of `AND` was used rather than validating that
it was used correctly.

pkg/tsdb/influxdb/query.go

@@ -151,8 +151,12 @@ func (query *Query) renderMeasurement() string {
 func (query *Query) renderWhereClause() string {
 	res := " WHERE "
 	conditions := query.renderTags()
-	res += strings.Join(conditions, " ")
 	if len(conditions) > 0 {
+		if len(conditions) > 1 {
+			res += "(" + strings.Join(conditions, " ") + ")"
+		} else {
+			res += conditions[0]
+		}
 		res += " AND "
 	}
 

pkg/tsdb/influxdb/query_test.go

@@ -57,7 +57,7 @@ func TestInfluxdbQueryBuilder(t *testing.T) {
 
 			rawQuery, err := query.Build(queryContext)
 			So(err, ShouldBeNil)
-			So(rawQuery, ShouldEqual, `SELECT mean("value") FROM "cpu" WHERE "hostname" = 'server1' OR "hostname" = 'server2' AND time > now() - 5m GROUP BY time(5s), "datacenter" fill(null)`)
+			So(rawQuery, ShouldEqual, `SELECT mean("value") FROM "cpu" WHERE ("hostname" = 'server1' OR "hostname" = 'server2') AND time > now() - 5m GROUP BY time(5s), "datacenter" fill(null)`)
 		})
 
 		Convey("can build query with math part", func() {