WHERE returning entire table - sql

Question

Question: How do I ignore WHERE param if value = '0' or NULL
One of the columns returned is showing 0 which is causing problems in my query.
The problem I am having is in the p.author value. Sometimes it matches up with a pe.system_id, but sometimes it is 0 or NULL. If p.author is 0. If I comment the and param out, then it returns a row for each entry in docsadm.people pe1 or nothing because no entry = 0
SELECT
p.docnumber, p.docname, p.abstract, d.type_id, a.application,
pe1.full_name as 'Author', pe.full_name as 'Registered by',
convert(varchar(10), p.pif_letter_date + 0.4166666,111) as 'Date written',
convert(varchar(10), p.creation_date + 0.4166666,111) as 'Registered on',
convert(varchar(10), p.last_edit_date + 0.4166666,111) as 'Last edit date',
f.pd_filept_no, f.pd_file_name, f.pd_title, sm.pif_marking, s.pd_section_code,
p.status as 'Availability', p.related, p.kmc_old_docno
FROM
docsadm.profile p, docsadm.pd_file_part f, docsadm.people pe,
docsadm.people pe1, docsadm.apps a, docsadm.documenttypes d,
docsadm.pif_sec_mark sm, docsadm.pd_section s
WHERE
p.DOCNUMBER IN ('5451326')
AND p.pd_file_part = f.system_id
AND p.typist = pe.system_id
AND p.author = pe1.system_id --Problem Line
AND p.application = a.system_id
AND p.documenttype = d.system_id
AND f.kmc_ptto_sec_mark = sm.system_id
AND f.pd_pttosec_link = s.system_id
AND p.item_type IN ('D','E','M','F')
ORDER BY
5, 4, 1

Answer 1

There are a number of ways but the way I prefer is to use the JOIN .. ON syntax and make tables with optional data part of a LEFT OUTER JOIN (LEFT JOIN).
SELECT p.docnumber,
p.docname,
p.abstract,
d.type_id,
a.application,
pe1.full_name as 'Author',
pe.full_name as 'Registered by',
convert(varchar(10), p.pif_letter_date + 0.4166666,111) as 'Date written',
convert(varchar(10), p.creation_date + 0.4166666,111) as 'Registered on',
convert(varchar(10), p.last_edit_date + 0.4166666,111) as 'Last edit date',
f.pd_filept_no,
f.pd_file_name,
f.pd_title,
sm.pif_marking,
s.pd_section_code,
p.status as 'Availability',
p.related,
p.kmc_old_docno
FROM docsadm.profile p
JOIN docsadm.pd_file_part f
ON p.pd_file_part = f.system_id
JOIN docsadm.people pe
ON p.typist = pe.system_id
JOIN docsadm.apps a
ON p.application = a.system_id
JOIN docsadm.documenttypes d
ON p.documenttype = d.system_id
JOIN docsadm.pif_sec_mark sm
ON f.kmc_ptto_sec_mark = sm.system_id
JOIN docsadm.pd_section s
ON f.pd_pttosec_link = s.system_id
LEFT
JOIN docsadm.people pe1
ON p.author = pe1.system_id --Problem Line
WHERE p.DOCNUMBER in ('5451326')
and p.item_type in ('D','E','M','F')
ORDER by 5, 4, 1

Answer 2

...
and ( (p.author is null) or (p.author='0') or (p.author=pe1.system_id) )
...
...work?
If p.author is null or p.author=0 it will turn that "and ..." into "and true"