>>Try

>>SET grno=NVL(ID.grno,SPACE(6)) ;
>>

>>>
>>>trying to update table using UPDATE-SQL and keep getting an error, that field "grno" doe snot accept NULL value.
>>>First of all, it happens only when I run EXE, never in APP. and second, I am using NVL function to prevent any NULLs.
>>>
>>>Please see the simple code below:
>>>UPDATE PS1;
>>> SET PS1.grno=NVL(ID.grno,SPACE(6)) ;
>>> FROM PS1 ;
>>> LEFT OUTER JOIN ID1 ON UPPER(PS1.employeeid)=UPPER(ID1.employeeid)
>>>
>>>I tried to use INNER JOIN, but received the same error message.
>>>
>>>And by the way, I modified the table PS1 to allow NULL value in the field "grno".
>>>
>>>Any ideas?
>>>
>>>Thanks
>>>Jerry
>>>
>
>
>Thanks Sergey, same error.

SET grno=NVL(ID1.grno,SPACE(6)) ;

You had a wrong alias there, used ID instead of ID1.