TimeZone shift problem in Flink SQL

[徐涛]

Hi Experts,
        I have the following two UDFs,
        unix_timestamp:   transform from string to Timestamp, with the 
arguments (value:String, format:String), return Timestamp
       from_unixtime:    transform from Timestamp to String, with the arguments 
(ts:Long, format:String), return String


        select 
         number,
         ts,
         from_unixtime(unix_timestamp(LAST_UPDATE_TIME, 'EEE MMM dd HH:mm:Ss z 
yyyy'),'yyyy-MM-dd')  as dt
      from 
         test;

     when the LAST_UPDATE_TIME value is "Tue Jan 22 21:03:12 CST 2019”, the 
unix_timestamp return a Timestamp with value 1548162182001.
      but when from_unixtime is invoked, the timestamp with value 1548190982001 
is passed in, there are 8 hours shift between them.
      May I know why there are 8 hours shift between them, and how can I get 
the timestamp that are passed out originally from the first UDF without 
changing the code?
        
      Thanks very much.

Best
Henry