fix sqlstr released issue

src/client/src/tscPrepare.c

@@ -48,6 +48,7 @@ typedef struct SMultiTbStmt {
   bool      nameSet;
   bool      tagSet;
   uint64_t  currentUid;
+  char     *sqlstr;
   uint32_t  tbNum;
   SStrToken tbname;
   SStrToken stbname;
@@ -1291,6 +1292,7 @@ int stmtParseInsertTbTags(SSqlObj* pSql, STscStmt* pStmt) {
     }
 
     pStmt->mtb.values = sToken;
+
   }
 
   return TSDB_CODE_SUCCESS;
@@ -1373,7 +1375,12 @@ int stmtGenInsertStatement(SSqlObj* pSql, STscStmt* pStmt, const char* name, TAO
     break;
   }
 
-  free(pSql->sqlstr);
+  if (pStmt->mtb.sqlstr == NULL) {
+    pStmt->mtb.sqlstr = pSql->sqlstr;
+  } else {
+    tfree(pSql->sqlstr);
+  }
+  
   pSql->sqlstr = str;
 
   return TSDB_CODE_SUCCESS;
@@ -1633,6 +1640,7 @@ int taos_stmt_close(TAOS_STMT* stmt) {
       taosHashCleanup(pStmt->pSql->cmd.insertParam.pTableBlockHashList);
       pStmt->pSql->cmd.insertParam.pTableBlockHashList = NULL;
       taosArrayDestroy(pStmt->mtb.tags);
+      tfree(pStmt->mtb.sqlstr);
     }
   }