I have a column that is specifyed as (int, not null). I've been trying to insert NULL for the missing records of that column, can anyone give me a hint?
No you cant insert
NULL in a
NON NULL column. That's what constraints are for.
If you want, you can alter the column.
ALTER TABLE dbo.mytable ALTER COLUMN column_a INT NULL
Or just insert 0 for each record you don't want to have a value.
Though be aware on the difference of NULL and blank/zero values.