When you use the comparison operators in SQL with the Where clause, you can remove the columns with null values. If you need the values with null too, then you need to use the appropriate ISNull
function as follows:
where IsNull(columnname, value) not like 'comparisonValue'
with the correct column name and value
with something like 'comparisonValue' & 'extraText'
The extraText is just to ensure that you don't end up fetching a record that exactly matches the replacement value.