feature(query):add lastrow scan operator.

source/dnode/vnode/CMakeLists.txt

@@ -46,6 +46,7 @@ target_sources(
     "src/tsdb/tsdbReaderWriter.c"
     "src/tsdb/tsdbUtil.c"
     "src/tsdb/tsdbSnapshot.c"
+    "src/tsdb/tsdbCacheRead.c"
 
     # tq
     "src/tq/tq.c"

source/libs/executor/inc/executorimpl.h

@@ -285,6 +285,12 @@ typedef struct STagScanInfo {
   SNode*           pFilterNode;  // filter info,
 } STagScanInfo;
 
+typedef struct SLastrowScanInfo {
+  SSDataBlock    *pRes;
+  STableListInfo *pTableList;
+  SReadHandle     readHandle;
+} SLastrowScanInfo;
+
 typedef enum EStreamScanMode {
   STREAM_SCAN_FROM_READERHANDLE = 1,
   STREAM_SCAN_FROM_RES,

source/libs/executor/src/scanoperator.c

@@ -2343,3 +2343,68 @@ _error:
   taosMemoryFree(pOperator);
   return NULL;
 }
+
+static SSDataBlock* doScanLastrow(SOperatorInfo* pOperator) {
+  if (pOperator->status == OP_EXEC_DONE) {
+    return NULL;
+  }
+
+  SLastrowScanInfo* pInfo = pOperator->info;
+  SExecTaskInfo* pTaskInfo = pOperator->pTaskInfo;
+
+  int32_t size = taosArrayGetSize(pInfo->pTableList->pTableList);
+  if (size == 0) {
+    setTaskStatus(pTaskInfo, TASK_COMPLETED);
+    return NULL;
+  }
+
+  // check if it is a group by tbname
+  if (size == taosHashGetSize(pInfo->pTableList->map)) {
+    // fetch last row for each table
+  } else {
+    //todo fetch the result for each group
+
+  }
+
+  return pInfo->pRes->info.rows == 0? NULL:pInfo->pRes;
+}
+
+static void destroyLastrowScanOperator(void* param, int32_t numOfOutput) {
+  SLastrowScanInfo* pInfo = (SLastrowScanInfo*) param;
+  blockDataDestroy(pInfo->pRes);
+}
+
+SOperatorInfo* createLastrowScanOperator(STableScanPhysiNode* pTableScanNode, SReadHandle* readHandle,
+    STableListInfo* pTableList, SExecTaskInfo* pTaskInfo) {
+
+  SLastrowScanInfo* pInfo = taosMemoryCalloc(1, sizeof(SLastrowScanInfo));
+  SOperatorInfo*    pOperator = taosMemoryCalloc(1, sizeof(SOperatorInfo));
+  if (pInfo == NULL || pOperator == NULL) {
+    goto _error;
+  }
+
+  pInfo->pTableList = pTableList;
+  pInfo->readHandle = *readHandle;
+//  pInfo->pRes = createResDataBlock();
+
+  pOperator->name         = "LastrowScanOperator";
+//  pOperator->operatorType = QUERY_NODE_PHYSICAL_PLAN_TABLE_MERGE_SCAN;
+  pOperator->blocking     = false;
+  pOperator->status       = OP_NOT_OPENED;
+  pOperator->info         = pInfo;
+  pOperator->pTaskInfo    = pTaskInfo;
+
+  initResultSizeInfo(pOperator, 1024);
+
+  pOperator->fpSet =
+      createOperatorFpSet(operatorDummyOpenFn, doScanLastrow, NULL, NULL, destroyLastrowScanOperator,
+                          NULL, NULL, NULL);
+  pOperator->cost.openCost = 0;
+  return pOperator;
+
+_error:
+  pTaskInfo->code = TSDB_CODE_OUT_OF_MEMORY;
+  taosMemoryFree(pInfo);
+  taosMemoryFree(pOperator);
+  return NULL;
+}