refactor(query):check for none table.

source/dnode/vnode/src/tsdb/tsdbRead.c

@@ -3507,45 +3507,47 @@ int32_t tsdbReaderOpen(SVnode* pVnode, SQueryTableDataCond* pCond, SArray* pTabl
     goto _err;
   }
 
-  code = tsdbTakeReadSnap(pReader->pTsdb, &pReader->pReadSnap);
-  if (code != TSDB_CODE_SUCCESS) {
-    goto _err;
-  }
+  if (numOfTables > 0) {
+    code = tsdbTakeReadSnap(pReader->pTsdb, &pReader->pReadSnap);
+    if (code != TSDB_CODE_SUCCESS) {
+      goto _err;
+    }
 
-  if (pReader->type == TIMEWINDOW_RANGE_CONTAINED) {
-    SDataBlockIter* pBlockIter = &pReader->status.blockIter;
+    if (pReader->type == TIMEWINDOW_RANGE_CONTAINED) {
+      SDataBlockIter* pBlockIter = &pReader->status.blockIter;
 
-    initFilesetIterator(&pReader->status.fileIter, pReader->pReadSnap->fs.aDFileSet, pReader);
-    resetDataBlockIterator(&pReader->status.blockIter, pReader->order);
+      initFilesetIterator(&pReader->status.fileIter, pReader->pReadSnap->fs.aDFileSet, pReader);
+      resetDataBlockIterator(&pReader->status.blockIter, pReader->order);
 
-    // no data in files, let's try buffer in memory
-    if (pReader->status.fileIter.numOfFiles == 0) {
-      pReader->status.loadFromFile = false;
+      // no data in files, let's try buffer in memory
+      if (pReader->status.fileIter.numOfFiles == 0) {
+        pReader->status.loadFromFile = false;
+      } else {
+        code = initForFirstBlockInFile(pReader, pBlockIter);
+        if (code != TSDB_CODE_SUCCESS) {
+          return code;
+        }
+      }
     } else {
-      code = initForFirstBlockInFile(pReader, pBlockIter);
+      STsdbReader*    pPrevReader = pReader->innerReader[0];
+      SDataBlockIter* pBlockIter = &pPrevReader->status.blockIter;
+
+      code = tsdbTakeReadSnap(pPrevReader->pTsdb, &pPrevReader->pReadSnap);
       if (code != TSDB_CODE_SUCCESS) {
-        return code;
+        goto _err;
       }
-    }
-  } else {
-    STsdbReader*    pPrevReader = pReader->innerReader[0];
-    SDataBlockIter* pBlockIter = &pPrevReader->status.blockIter;
 
-    code = tsdbTakeReadSnap(pPrevReader->pTsdb, &pPrevReader->pReadSnap);
-    if (code != TSDB_CODE_SUCCESS) {
-      goto _err;
-    }
+      initFilesetIterator(&pPrevReader->status.fileIter, pPrevReader->pReadSnap->fs.aDFileSet, pPrevReader);
+      resetDataBlockIterator(&pPrevReader->status.blockIter, pPrevReader->order);
 
-    initFilesetIterator(&pPrevReader->status.fileIter, pPrevReader->pReadSnap->fs.aDFileSet, pPrevReader);
-    resetDataBlockIterator(&pPrevReader->status.blockIter, pPrevReader->order);
-
-    // no data in files, let's try buffer in memory
-    if (pPrevReader->status.fileIter.numOfFiles == 0) {
-      pPrevReader->status.loadFromFile = false;
-    } else {
-      code = initForFirstBlockInFile(pPrevReader, pBlockIter);
-      if (code != TSDB_CODE_SUCCESS) {
-        return code;
+      // no data in files, let's try buffer in memory
+      if (pPrevReader->status.fileIter.numOfFiles == 0) {
+        pPrevReader->status.loadFromFile = false;
+      } else {
+        code = initForFirstBlockInFile(pPrevReader, pBlockIter);
+        if (code != TSDB_CODE_SUCCESS) {
+          return code;
+        }
       }
     }
   }
@@ -3604,6 +3606,10 @@ void tsdbReaderClose(STsdbReader* pReader) {
     taosMemoryFree(pLReader);
   }
 
+  if (pReader->innerReader[0] != 0) {
+    tsdbUntakeReadSnap(pReader->innerReader[0]->pTsdb, pReader->innerReader[0]->pReadSnap);
+  }
+
   tsdbDebug(
       "%p :io-cost summary: head-file:%" PRIu64 ", head-file time:%.2f ms, SMA:%" PRId64
       " SMA-time:%.2f ms, fileBlocks:%" PRId64 ", fileBlocks-load-time:%.2f ms, "