enh: make single_stable mode work

include/util/taoserror.h

@@ -244,9 +244,10 @@ int32_t* taosGetErrno();
 #define TSDB_CODE_MND_TOO_MANY_COLUMNS          TAOS_DEF_ERROR_CODE(0, 0x03AC)
 #define TSDB_CODE_MND_COLUMN_ALREADY_EXIST      TAOS_DEF_ERROR_CODE(0, 0x03AD)
 #define TSDB_CODE_MND_COLUMN_NOT_EXIST          TAOS_DEF_ERROR_CODE(0, 0x03AE)
+#define TSDB_CODE_MND_SINGLE_STB_MODE_DB        TAOS_DEF_ERROR_CODE(0, 0x03B0)
 
 // mnode-infoSchema
-#define TSDB_CODE_MND_INVALID_SYS_TABLENAME         TAOS_DEF_ERROR_CODE(0, 0x03B0)
+#define TSDB_CODE_MND_INVALID_SYS_TABLENAME         TAOS_DEF_ERROR_CODE(0, 0x03BA)
 
 // mnode-func
 #define TSDB_CODE_MND_FUNC_ALREADY_EXIST        TAOS_DEF_ERROR_CODE(0, 0x03C0)

source/dnode/mnode/impl/inc/mndStb.h

@@ -29,6 +29,7 @@ void     mndReleaseStb(SMnode *pMnode, SStbObj *pStb);
 SSdbRaw *mndStbActionEncode(SStbObj *pStb);
 int32_t  mndValidateStbInfo(SMnode *pMnode, SSTableMetaVersion *pStbs, int32_t numOfStbs, void **ppRsp,
                             int32_t *pRspLen);
+int32_t  mndGetNumOfStbs(SMnode *pMnode, char *dbName, int32_t *pNumOfStbs);
 
 #ifdef __cplusplus
 }

source/dnode/mnode/impl/src/mndStb.c

@@ -774,6 +774,13 @@ static int32_t mndProcessMCreateStbReq(SNodeMsg *pReq) {
     goto _OVER;
   }
 
+  int32_t numOfStbs = -1;
+  mndGetNumOfStbs(pMnode, pDb->name, &numOfStbs);
+  if (pDb->cfg.numOfStables == 1 && numOfStbs != 0 ) {
+    terrno = TSDB_CODE_MND_SINGLE_STB_MODE_DB;
+    goto _OVER;
+  }
+
   code = mndCreateStb(pMnode, pReq, &createReq, pDb);
   if (code == 0) code = TSDB_CODE_MND_ACTION_IN_PROGRESS;
 
@@ -1579,7 +1586,7 @@ int32_t mndValidateStbInfo(SMnode *pMnode, SSTableMetaVersion *pStbVersions, int
   return 0;
 }
 
-static int32_t mndGetNumOfStbs(SMnode *pMnode, char *dbName, int32_t *pNumOfStbs) {
+int32_t mndGetNumOfStbs(SMnode *pMnode, char *dbName, int32_t *pNumOfStbs) {
   SSdb   *pSdb = pMnode->pSdb;
   SDbObj *pDb = mndAcquireDb(pMnode, dbName);
   if (pDb == NULL) {

source/util/src/terror.c

@@ -250,6 +250,7 @@ TAOS_DEFINE_ERROR(TSDB_CODE_MND_TAG_NOT_EXIST,            "Tag does not exist")
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_TOO_MANY_COLUMNS,         "Too many columns")
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_COLUMN_ALREADY_EXIST,     "Column already exists")
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_COLUMN_NOT_EXIST,         "Column does not exist")
+TAOS_DEFINE_ERROR(TSDB_CODE_MND_SINGLE_STB_MODE_DB,       "Database is single stable mode")
 
 // mnode-infoSchema
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_INVALID_SYS_TABLENAME,    "Invalid system table name")