Merge pull request #14827 from taosdata/feature/3.0_debug_wxy

feat: the 'null' value for the user is of type 'varchar(0)'

source/libs/function/src/builtins.c

@@ -1976,7 +1976,7 @@ const SBuiltinFuncDefinition funcMgtBuiltins[] = {
   {
     .name = "leastsquares",
     .type = FUNCTION_TYPE_LEASTSQUARES,
-    .classification = FUNC_MGT_AGG_FUNC | FUNC_MGT_FORBID_STREAM_FUNC,
+    .classification = FUNC_MGT_AGG_FUNC | FUNC_MGT_TIMELINE_FUNC | FUNC_MGT_FORBID_STREAM_FUNC,
     .translateFunc = translateLeastSQR,
     .getEnvFunc   = getLeastSQRFuncEnv,
     .initFunc     = leastSQRFunctionSetup,

source/libs/parser/src/parCalcConst.c

@@ -218,7 +218,7 @@ static SNode* createConstantValue() {
 static int32_t calcConstProjections(SCalcConstContext* pCxt, SSelectStmt* pSelect, bool subquery) {
   SNode* pProj = NULL;
   WHERE_EACH(pProj, pSelect->pProjectionList) {
-    if (subquery && isUselessCol((SExprNode*)pProj)) {
+    if (subquery && !pSelect->isDistinct && isUselessCol((SExprNode*)pProj)) {
       ERASE_NODE(pSelect->pProjectionList);
       continue;
     }

source/libs/parser/src/parTranslater.c

@@ -4757,8 +4757,13 @@ static int32_t extractQueryResultSchema(const SNodeList* pProjections, int32_t*
   int32_t index = 0;
   FOREACH(pNode, pProjections) {
     SExprNode* pExpr = (SExprNode*)pNode;
-    (*pSchema)[index].type = pExpr->resType.type;
-    (*pSchema)[index].bytes = pExpr->resType.bytes;
+    if (TSDB_DATA_TYPE_NULL == pExpr->resType.type) {
+      (*pSchema)[index].type = TSDB_DATA_TYPE_VARCHAR;
+      (*pSchema)[index].bytes = 0;
+    } else {
+      (*pSchema)[index].type = pExpr->resType.type;
+      (*pSchema)[index].bytes = pExpr->resType.bytes;
+    }
     (*pSchema)[index].colId = index + 1;
     if ('\0' != pExpr->userAlias[0]) {
       strcpy((*pSchema)[index].name, pExpr->userAlias);