Table is modified by DataFrameWriter

[guoqing0...@yahoo.com.hk]

Hi all,
I found the table structure was modified  when use DataFrameWriter.jdbc to save 
the content of DataFrame , 
 
sqlContext.sql("select '2015-09-17',count(1) from 
test").write.jdbc(url,test,properties)

table structure before saving:
app_key text
t_amount bigint(20)

saved:
_c0 text
_c1 bigint(20)

Is there any way to just save the field in sequence and do not alter the table 
? 

Thanks!