fix: the problem of null in case when expression

source/libs/parser/src/parTranslater.c

@@ -1878,6 +1878,7 @@ static int32_t rewriteIsTrue(SNode* pSrc, SNode** pIsTrue) {
 
 static EDealRes translateCaseWhen(STranslateContext* pCxt, SCaseWhenNode* pCaseWhen) {
   bool   first = true;
+  bool   allNullThen = true;
   SNode* pNode = NULL;
   FOREACH(pNode, pCaseWhen->pWhenThenList) {
     SWhenThenNode* pWhenThen = (SWhenThenNode*)pNode;
@@ -1889,12 +1890,28 @@ static EDealRes translateCaseWhen(STranslateContext* pCxt, SCaseWhenNode* pCaseW
       }
       pWhenThen->pWhen = pIsTrue;
     }
-    if (first || dataTypeComp(&pCaseWhen->node.resType, &((SExprNode*)pNode)->resType) < 0) {
-      pCaseWhen->node.resType = ((SExprNode*)pNode)->resType;
+
+    SExprNode* pThenExpr = (SExprNode*)pNode;
+    if (TSDB_DATA_TYPE_NULL == pThenExpr->resType.type) {
+      continue;
+    }
+    allNullThen = false;
+    if (first || dataTypeComp(&pCaseWhen->node.resType, &pThenExpr->resType) < 0) {
+      pCaseWhen->node.resType = pThenExpr->resType;
     }
     first = false;
   }
 
+  if (allNullThen) {
+    if (NULL != pCaseWhen->pElse) {
+      pCaseWhen->node.resType = ((SExprNode*)pCaseWhen->pElse)->resType;
+    } else {
+      pCaseWhen->node.resType.type = TSDB_DATA_TYPE_NULL;
+      pCaseWhen->node.resType.bytes = tDataTypes[TSDB_DATA_TYPE_NULL].bytes;
+      return DEAL_RES_CONTINUE;
+    }
+  }
+
   FOREACH(pNode, pCaseWhen->pWhenThenList) {
     SWhenThenNode* pWhenThen = (SWhenThenNode*)pNode;
     if (!dataTypeEqual(&pCaseWhen->node.resType, &((SExprNode*)pNode)->resType)) {