[add case]

tests/script/tsim/query/stddev.sim

+system sh/stop_dnodes.sh
+
+system sh/deploy.sh -n dnode1 -i 1
+system sh/cfg.sh -n dnode1 -c walLevel -v 1
+system sh/exec.sh -n dnode1 -s start
+
+$loop_cnt = 0
+check_dnode_ready:
+	$loop_cnt = $loop_cnt + 1
+	sleep 200
+	if $loop_cnt == 10 then
+	  print ====> dnode not ready!
+		return -1
+	endi
+sql show dnodes
+print ===> $rows $data00 $data01 $data02 $data03 $data04 $data05
+if $data00 != 1 then
+  return -1
+endi
+if $data04 != ready then
+  goto check_dnode_ready
+endi
+
+sql connect
+
+$dbPrefix = db
+$tbPrefix = ct
+$mtPrefix = stb
+$tbNum = 10
+$rowNum = 20
+$totalNum = 200
+
+print =============== step1
+$i = 0
+$db = $dbPrefix . $i
+$mt = $mtPrefix . $i
+
+sql drop database $db -x step1
+step1:
+sql create database $db
+sql use $db
+sql create table $mt (ts timestamp, tbcol int) TAGS(tgcol int)
+
+$i = 0
+while $i < $tbNum
+  $tb = $tbPrefix . $i
+  sql create table $tb using $mt tags( $i )
+  
+  $x = 0
+  while $x < $rowNum
+    $cc = $x * 60000
+    $ms = 1601481600000 + $cc
+
+    sql insert into $tb values ($ms , $x ) 
+    $x = $x + 1
+  endw 
+ 
+  $i = $i + 1
+endw 
+
+sleep 100
+
+print =============== step2
+$i = 1
+$tb = $tbPrefix . $i
+
+sql select stddev(tbcol) from $tb
+print ===> $data00
+if $data00 != 5.766281297 then 
+  return -1
+endi
+
+print =============== step3
+$cc = 4 * 60000
+$ms = 1601481600000 + $cc
+
+print ===> select stddev(tbcol) from $tb where ts <= $ms
+sql select stddev(tbcol) from $tb where ts <= $ms
+print ====> $data00 $data01 $data02 $data03 $data04 $data05
+if $data00 != 1.414213562 then 
+  return -1
+endi
+
+print =============== step4
+sql select stddev(tbcol) as b from $tb
+print ===> $data00
+if $data00 != 5.766281297 then 
+  return -1
+endi
+
+print =============== step5
+sql select stddev(tbcol) as b from $tb interval(1m)
+print ===> $data01 
+if $data01 != 0.000000000 then 
+  return -1
+endi
+
+sql select stddev(tbcol) as b from $tb interval(1d)
+print ===> $data01
+if $data01 != 5.766281297 then 
+  return -1
+endi
+
+print =============== step6
+$cc = 4 * 60000
+$ms = 1601481600000 + $cc
+
+sql select stddev(tbcol) as b from $tb where ts <= $ms interval(1m)
+print ===> $data01
+if $data01 != 0.000000000 then 
+  return -1
+endi
+if $rows != 5 then 
+  return -1
+endi
+
+print =============== clear
+sql drop database $db
+sql show databases
+if $rows != 0 then 
+  return -1
+endi
+
+system sh/exec.sh -n dnode1 -s stop -x SIGINT
\ No newline at end of file