feat(universe): support for dynamic queries (#1284)

stdlib/testing/testdata/dynamic_query.flux

@@ -0,0 +1,39 @@
+package testdata_test
+
+import "testing"
+
+option now = () => (2030-01-01T00:00:00Z)
+
+inData = "
+#datatype,string,long,dateTime:RFC3339,double,string,string
+#group,false,false,false,false,true,true
+#default,_result,,,,,
+,result,table,_time,_value,_measurement,user
+,,0,2018-05-22T19:53:26Z,0,CPU,user1
+,,0,2018-05-22T19:53:36Z,1,CPU,user1
+,,1,2018-05-22T19:53:26Z,4,CPU,user2
+,,1,2018-05-22T19:53:36Z,20,CPU,user2
+,,1,2018-05-22T19:53:46Z,7,CPU,user2
+,,2,2018-05-22T19:53:26Z,1,RAM,user1"
+
+outData = "
+#datatype,string,long,dateTime:RFC3339,double,string,string
+#group,false,false,false,false,true,true
+#default,_result,,,,,
+,result,table,_time,_value,_measurement,user
+,,0,2018-05-22T19:53:26Z,0,CPU,user1
+,,0,2018-05-22T19:53:36Z,1,CPU,user1
+,,1,2018-05-22T19:53:26Z,1,RAM,user1
+"
+
+t_dynamic = (table=<-) => {
+    r = table |> range(start: 2018-05-22T19:53:26Z) |> drop(columns: ["_start", "_stop"])
+    t = r |> tableFind(fn: (key) => key._measurement == "CPU")
+    users = t |> getColumn(column: "user")
+
+    // This is a dynamic query, because this query uses the results of another one.
+    return r |> filter(fn: (r) => contains(value: r.user, set: users))
+}
+
+test _dynamic_query = () =>
+	({input: testing.loadStorage(csv: inData), want: testing.loadMem(csv: outData), fn: t_dynamic})