diff --git a/src/client/src/tscParseInsert.c b/src/client/src/tscParseInsert.c
index 05b8b031d99c2b0f4e54e9fc3392a20a9e1bcfcc..de974bec46426a892b9c645a95c7b959ac97d9ff 100644
--- a/src/client/src/tscParseInsert.c
+++ b/src/client/src/tscParseInsert.c
@@ -360,7 +360,7 @@ int32_t tsParseOneColumn(SSchema *pSchema, SStrToken *pToken, char *payload, cha
         return tscInvalidOperationMsg(msg, "json tag length too long", pToken->z);
       }
       if (pToken->type == TK_NULL) {
-        *(int8_t *)payload = TSDB_DATA_TINYINT_NULL;
+        *(int8_t *)payload = TSDB_DATA_JSON_PLACEHOLDER;
       } else if (pToken->type != TK_STRING){
         tscInvalidOperationMsg(msg, "invalid json data", pToken->z);
       } else{
@@ -1063,7 +1063,7 @@ static int32_t tscCheckIfCreateTable(char **sqlstr, SSqlObj *pSql, char** boundC
         sToken.n -= 2;
       }
 
-      char tagVal[TSDB_MAX_TAGS_LEN];
+      char tagVal[TSDB_MAX_TAGS_LEN] = {0};
       code = tsParseOneColumn(pSchema, &sToken, tagVal, pInsertParam->msg, &sql, false, tinfo.precision);
       if (code != TSDB_CODE_SUCCESS) {
         tdDestroyKVRowBuilder(&kvRowBuilder);
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index b045c566f1a72b8f0ca970d8e30d1b0e6486be68..4d63438c9a5582981b86e41599b6b3a30314c9c9 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -6871,7 +6871,7 @@ int32_t setAlterTableInfo(SSqlObj* pSql, struct SSqlInfo* pInfo) {
     }
     SKVRowBuilder kvRowBuilder = {0};
     if (pTagsSchema->type == TSDB_DATA_TYPE_JSON) {
-      if (pItem->pVar.nType != TSDB_DATA_TYPE_BINARY) {
+      if (pItem->pVar.nType != TSDB_DATA_TYPE_BINARY && pItem->pVar.nType != TSDB_DATA_TYPE_NULL) {
         tscError("json type error, should be string");
         return invalidOperationMsg(pMsg, msg25);
       }
@@ -8714,7 +8714,7 @@ int32_t doCheckForCreateFromStable(SSqlObj* pSql, SSqlInfo* pInfo) {
         return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg5);
       }
       tVariantListItem* pItem = taosArrayGet(pValList, 0);
-      if(pItem->pVar.nType != TSDB_DATA_TYPE_BINARY){
+      if(pItem->pVar.nType != TSDB_DATA_TYPE_BINARY && pItem->pVar.nType != TSDB_DATA_TYPE_NULL){
         tscError("json type error, should be string");
         tdDestroyKVRowBuilder(&kvRowBuilder);
         return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg7);
@@ -8724,6 +8724,7 @@ int32_t doCheckForCreateFromStable(SSqlObj* pSql, SSqlInfo* pInfo) {
         tdDestroyKVRowBuilder(&kvRowBuilder);
         return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg3);
       }
+
       ret = parseJsontoTagData(pItem->pVar.pz, &kvRowBuilder, tscGetErrorMsgPayload(pCmd), pTagSchema[0].colId);
       if (ret != TSDB_CODE_SUCCESS) {
         tdDestroyKVRowBuilder(&kvRowBuilder);
diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index e96e3c16da84b3ffc25b33e3864c4e38dcc3977f..322413a3cd7e637c477903b09522f60c11056885 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -5459,7 +5459,7 @@ int parseJsontoTagData(char* json, SKVRowBuilder* kvRowBuilder, char* errMsg, in
   varDataSetLen(nullTypeVal + CHAR_BYTES, INT_BYTES);
   *(uint32_t*)(varDataVal(nullTypeKey)) = jsonNULL;
   tdAddColToKVRow(kvRowBuilder, jsonIndex++, TSDB_DATA_TYPE_NCHAR, nullTypeKey, false);   // add json null type
-  if (strtrim(json) == 0 || strcasecmp(json, "null") == 0){
+  if (!json || strtrim(json) == 0 || strcasecmp(json, "null") == 0){
     *(uint32_t*)(varDataVal(nullTypeVal + CHAR_BYTES)) = jsonNULL;
     tdAddColToKVRow(kvRowBuilder, jsonIndex++, TSDB_DATA_TYPE_NCHAR, nullTypeVal, true);   // add json null value
     return TSDB_CODE_SUCCESS;
diff --git a/src/common/src/tvariant.c b/src/common/src/tvariant.c
index 0d00856f9be76ee917d12ff7435142d6d55ccecf..3c9d62294776bfa639620249416eee738fe24b99 100644
--- a/src/common/src/tvariant.c
+++ b/src/common/src/tvariant.c
@@ -953,7 +953,7 @@ int32_t tVariantDumpEx(tVariant *pVariant, char *payload, int16_t type, bool inc
       break;
     }
     case TSDB_DATA_TYPE_JSON:{
-      if (pVariant->nType == TSDB_DATA_TYPE_BINARY){
+      if (pVariant->nType == TSDB_DATA_TYPE_BINARY || pVariant->nType == TSDB_DATA_TYPE_NULL){
         *((int8_t *)payload) = TSDB_DATA_JSON_PLACEHOLDER;
       } else if (pVariant->nType == TSDB_DATA_TYPE_JSON){   // select * from stable, set tag type to json，from setTagValue/tag_project_function
         memcpy(payload, pVariant->pz, pVariant->nLen);
diff --git a/tests/develop-test/0-others/json_tag.py b/tests/develop-test/0-others/json_tag.py
index b6a15ca770ea7e4885973a03bfc8e3bd08c3f54d..1271e8ae4a04e28bbe2d2f701524a3d42b1d0e61 100644
--- a/tests/develop-test/0-others/json_tag.py
+++ b/tests/develop-test/0-others/json_tag.py
@@ -22,9 +22,9 @@ import json
 class TDTestCase:
     def caseDescription(self):
         '''
-        Json tag test case, include create table with json tag,
-        select json tag and query with json tag in where condition,
-        besides, include json tag in group by/order by/join/subquery.
+        Json tag test case, include create table with json tag, select json tag and query with json tag in where condition, besides, include json tag in group by/order by/join/subquery.
+        case1: [TD-12452] fix error if json tag is NULL
+        case2: [TD-12389] describe child table, tag length error if the tag is json tag
         '''
         return
 
@@ -515,6 +515,23 @@ class TDTestCase:
         tdSql.query("select jtag->'tag3' from jsons1_16")
         tdSql.checkData(0, 0, '-2.111000000')
 
+        # test TD-12452
+        tdSql.execute("ALTER TABLE jsons1_1 SET TAG jtag=NULL")
+        tdSql.query("select jtag from jsons1_1")
+        tdSql.checkData(0, 0, None)
+        tdSql.execute("CREATE TABLE if not exists jsons1_20 using jsons1 tags(NULL)")
+        tdSql.query("select jtag from jsons1_20")
+        tdSql.checkData(0, 0, None)
+        tdSql.execute("insert into jsons1_21 using jsons1 tags(NULL) values(1591061628000, 11, false, '你就会','')")
+        tdSql.query("select jtag from jsons1_21")
+        tdSql.checkData(0, 0, None)
+
+        #test TD-12389
+        tdSql.query("describe jsons1")
+        tdSql.checkData(5, 2, 4096)
+        tdSql.query("describe jsons1_1")
+        tdSql.checkData(5, 2, 4096)
+
     def stop(self):
         tdSql.close()
         tdLog.success("%s successfully executed" % __file__)