[TS-1106]<fix>(query): '=' worked improperly if NULL contained in NCHAR type col

src/query/src/qFilter.c

@@ -3602,6 +3602,15 @@ int32_t filterConverNcharColumns(SFilterInfo* info, int32_t rows, bool *gotNchar
         char *src = FILTER_GET_COL_FIELD_DATA(fi, j);
         char *dst = FILTER_GET_COL_FIELD_DATA(&nfi, j);
         int32_t len = 0;
+        char *varSrc = varDataVal(src);
+        size_t k = 0, varSrcLen = varDataLen(src);
+        while (k < varSrcLen && varSrc[k++] == -1) {}
+        if (k == varSrcLen) {
+          /* NULL */
+          varDataLen(dst) = (VarDataLenT) varSrcLen;
+          varDataCopy(dst, src);
+          continue;
+        }
         bool ret = taosMbsToUcs4(varDataVal(src), varDataLen(src), varDataVal(dst), bufSize, &len);
         if(!ret) {
           qError("filterConverNcharColumns taosMbsToUcs4 error");

tests/pytest/fulltest.sh

@@ -289,6 +289,7 @@ python3 ./test.py -f query/bug6586.py
 # python3 ./test.py -f query/bug5903.py
 python3 ./test.py -f query/queryLimit.py
 python3 ./test.py -f query/queryPriKey.py
+python3 ./test.py -f query/queryNcharNull.py
 
 #stream
 python3 ./test.py -f stream/metric_1.py

tests/pytest/query/queryNcharNull.py

+###################################################################
+#           Copyright (c) 2016 by TAOS Technologies, Inc.
+#                     All rights reserved.
+#
+#  This file is proprietary and confidential to TAOS Technologies.
+#  No part of this file may be reproduced, stored, transmitted,
+#  disclosed or used in any form or by any means other than as
+#  expressly provided by the written permission from Jianhui Tao
+#
+###################################################################
+
+# -*- coding: utf-8 -*-
+
+import sys
+from util.log import *
+from util.cases import *
+from util.sql import *
+from util.dnodes import *
+
+
+class TDTestCase:
+    def init(self, conn, logSql):
+        tdLog.debug("start to execute %s" % __file__)
+        tdSql.init(conn.cursor(), logSql)
+
+    def run(self):
+        tdSql.prepare()
+        tdSql.execute("drop database if exists db")
+        tdSql.execute("create database if not exists db keep 3650")
+        tdSql.execute("use db")
+
+        tdSql.execute(
+            "create table stb1 (ts TIMESTAMP, id INT, col1 NCHAR(20), col2 BINARY(30), col3 FLOAT) TAGS (tid INT, name BINARY(20))"
+        )
+
+        tdSql.execute(
+            "insert into tb1 using stb1 tags(1, 'ABC') values (now - 1m, 1, '北京', '朝阳', 3.141)"
+        )
+
+        tdSql.execute(
+            "insert into tb1 using stb1 tags(1, 'ABC') values (now, 2, NULL, NULL, 3.141)"
+        )
+
+        tdSql.query(
+            "select * from (select * from stb1) where col1 = '北京'"
+        )
+
+        tdSql.checkData(0, 2, '北京') 
+
+        tdSql.execute(
+            "create table normal1 (ts TIMESTAMP, id INT, col1 NCHAR(20), col2 BINARY(30), col3 FLOAT)"
+        )
+
+        tdSql.execute(
+            "insert into normal1 values (now - 1m, 1, '北京', '朝阳', 3.141)"
+        )
+
+        tdSql.execute(
+            "insert into normal1 values (now, 1, NULL, NULL, 3.141)"
+        )
+
+        tdSql.query(
+            "select * from (select * from normal1) where col1 = '北京'"
+        )
+
+        tdSql.checkData(0, 2, '北京') 
+
+    def stop(self):
+        tdSql.close()
+        tdLog.success("%s successfully executed" % __file__)
+
+tdCases.addWindows(__file__, TDTestCase())
+tdCases.addLinux(__file__, TDTestCase())