SQL - how to consolidate Or statements - sql

Question

There must be a better way to write the query below, if you have any suggestions please let me know.
SELECT *
FROM
[eSDR_Full].[dbo].[course_register]
WHERE
broad_field_code = '08'
AND narrow_field_code = '05'
AND detail_field_code = '05'
AND end_month is null
AND disabled <> 'Y'
OR broad_field_code = '08'
AND narrow_field_code = '05'
AND detail_field_code = '05'
AND end_month > '201512'
AND disabled <> 'Y'
OR broad_field_code = '08'
AND narrow_field_code = '05'
AND detail_field_code = '05'
AND end_month is null
AND disabled is null
OR broad_field_code = '08'
AND narrow_field_code = '05'
AND detail_field_code = '05'
AND end_month > '201512'
AND disabled is null
ORDER BY
end_month DESC

Answer 1

First refactoring:
SELECT *
FROM [eSDR_Full].[dbo].[course_register]
Where (broad_field_code = '08' and narrow_field_code = '05' and detail_field_code = '05')
and ( (end_month is null and disabled <> 'Y')
or (end_month > '201512' and disabled <> 'Y')
or (end_month is null and disabled is null)
or (end_month > '201512' and disabled is null))
order by end_month desc
This makes it clear that you have a common prefix to all the conditions.
Second refactoring takes advantage of other commonalities:
SELECT *
FROM [eSDR_Full].[dbo].[course_register]
Where (broad_field_code = '08' and narrow_field_code = '05' and detail_field_code = '05')
and (end_month is null or end_month > '201512')
and (disabled is null or disabled <> 'Y')
order by end_month desc
Now it's clear that we just have a series of stacked ANDs based on simple conditions of one column each, so we can do this:
SELECT *
FROM [eSDR_Full].[dbo].[course_register]
Where broad_field_code = '08'
and narrow_field_code = '05'
and detail_field_code = '05'
and coalesce(end_month, '999999') > '201512'
and coalesce(disabled, 'N') <> 'Y')
order by end_month desc

Answer 2

This should work:
SELECT *
FROM [eSDR_Full].[dbo].[course_register]
WHERE broad_field_code = '08'
AND narrow_field_code = '05'
AND detail_field_code = '05'
AND (end_month IS NULL OR end_month > '201512')
AND ISNULL(disabled,'') != 'Y'
ORDER BY end_month DESC