fix issue in single meter subscription.

src/system/detail/src/vnodeShell.c

@@ -494,7 +494,11 @@ void vnodeExecuteRetrieveReq(SSchedMsg *pSched) {
     pMsg += sizeof(int32_t);
     *((int64_t*)pMsg) = htobe64(pQInfo->pObj->uid);
     pMsg += sizeof(int64_t);
+    if (pQInfo->pointsRead > 0) {
+      *((TSKEY*)pMsg) = htobe64(pQInfo->query.lastKey + 1);
+    } else {
       *((TSKEY*)pMsg) = htobe64(pQInfo->query.lastKey);
+    }
     pMsg += sizeof(TSKEY);
   }
 

tests/examples/c/subscribe.c

@@ -63,6 +63,11 @@ int main(int argc, char *argv[]) {
       keep = 0;
       continue;
     }
+    if (strncmp(argv[i], "-sql=", 5) == 0) {
+      sql = argv[i] + 5;
+      topic = "test-custom";
+      continue;
+    }
   }
 
   // init TAOS