Merge pull request #2291 from taosdata/hotfix/sangshuduo/alter-table-case

fix null/NULL issue in alter.sim

tests/script/general/parser/alter.sim

@@ -38,7 +38,7 @@ endi
 if $data02 != 1 then 
   return -1
 endi
-if $data03 != NULL then
+if $data03 != null then
   return -1
 endi
 sql alter table tb add column c3 nchar(4)
@@ -72,7 +72,7 @@ endi
 if $data02 != 1 then 
   return -1
 endi
-if $data03 != NULL then
+if $data03 != null then
   return -1
 endi
 
@@ -169,7 +169,7 @@ endi
 if $data01 != 2 then
   return -1
 endi
-if $data02 != NULL then
+if $data02 != null then
   return -1
 endi
 sql alter table mt add column c2 int
@@ -239,4 +239,4 @@ if $rows != 0 then
   return -1
 endi
 
-system sh/exec.sh -n dnode1 -s stop -x SIGINT
\ No newline at end of file
+system sh/exec.sh -n dnode1 -s stop -x SIGINT