sql - How to insert a null value to the database? -

my query doesn't work. says there syntax error near null keyword. dont know how fix it. want insert empty string or null database. how can it?
query

insert [remarks] values((select top 1 ref_no a_master order ref_no desc ), (select top 1 current_dept a_master order ref_no desc ),'630590', getdate()), null 

inner queries work without error.

you miss placed close brackets,it should this..

 insert [remarks]  values((select top 1 ref_no  a_master order ref_no desc ), (select top 1 current_dept  a_master order ref_no desc ),'630590', getdate(), null) 

in query u referred same table twice 2 column.

you can write like..

 insert [remarks] select top 1 ref_no,curent_dept   '630590',getdate(),null   a_master   order ref_no desc 

since both columns same table..