add test case to check sample result distribution

tests/pytest/fulltest.sh

@@ -345,6 +345,7 @@ python3 ./test.py -f functions/function_spread.py -r 1
 python3 ./test.py -f functions/function_stddev.py -r 1
 python3 ./test.py -f functions/function_sum.py -r 1
 python3 ./test.py -f functions/function_top.py -r 1
+python3 ./test.py -f functions/function_sample.py -r 1
 python3 ./test.py -f functions/function_twa.py -r 1
 python3 ./test.py -f functions/function_twa_test2.py
 python3 ./test.py -f functions/function_stddev_td2555.py

tests/pytest/functions/function_sample.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
+import taos
+from util.log import *
+from util.cases import *
+from util.sql import *
+import numpy as np
+import collections
+
+
+class TDTestCase:
+    def init(self, conn, logSql):
+        tdLog.debug("start to execute %s" % __file__)
+        tdSql.init(conn.cursor())
+
+        self.rowNum = 10
+        self.sample_times = 10000
+        self.ts = 1537146000000
+        
+    def run(self):
+        tdSql.prepare()
+
+        tdSql.execute('''create table test(ts timestamp, col1 tinyint, col2 smallint, col3 int, col4 bigint, col5 float, col6 double, 
+                    col7 bool, col8 binary(20), col9 nchar(20), col11 tinyint unsigned, col12 smallint unsigned, col13 int unsigned, col14 bigint unsigned) tags(loc nchar(20))''')
+        tdSql.execute("create table test1 using test tags('beijing')")
+        for i in range(self.rowNum):
+            tdSql.execute("insert into test1 values(%d, %d, %d, %d, %d, %f, %f, %d, 'taosdata%d', '涛思数据%d', %d, %d, %d, %d)" 
+                        % (self.ts + i, i, i + 1, i + 1, i + 1, i + 0.1, i + 0.1, i % 2, i + 1, i + 1, i + 1, i + 1, i + 1, i + 1))
+                     
+
+        print("begin sampling")
+        freqDict = collections.defaultdict(int)
+        for i in range(self.sample_times):
+            tdSql.query('select sample(col1, 2) from test1')
+            res1 = tdSql.getData(0, 1);
+            res2 = tdSql.getData(1, 1);
+            freqDict[res1] = freqDict[res1] + 1
+            freqDict[res2] = freqDict[res2] + 1
+        print("end sampling")
+
+        lower_bound = self.sample_times/5 - self.sample_times/50;
+        upper_bound = self.sample_times/5 + self.sample_times/50;
+        for i in range(self.rowNum):
+            print("{} are sampled in {} times", i, freqDict[i])
+
+            if not (freqDict[i]>lower_bound and freqDict[i]<upper_bound):
+                print("run it aggain, if it keeps appearing, sample function bug")
+                caller = inspect.getframeinfo(inspect.stack()[0][0])
+                args = (caller.filename, caller.lineno-2)
+                tdLog.exit("{}({}) failred. sample function failure".format(args[0], args[1]))
+                   
+    def stop(self):
+        tdSql.close()
+        tdLog.success("%s successfully executed" % __file__)
+
+tdCases.addWindows(__file__, TDTestCase())
+tdCases.addLinux(__file__, TDTestCase())