Regarding Distinct Keyword

hi guys i have a query that contains several table joins
when i run the query without select distinct x,y,z,w,.. or order by docno it takes around 20 second to finish execution, when i add select distinct x,y,z,w,.. or order by docno it ruturns the same result in just 2 seconds
is adding distict keyword or order by acts as an index for the query or what ?

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here is my query :




SELECT distinct p.indocno,p.CHAR_FIELD2_AR, p.CHAR_FIELD1, p.REVISION_NO, CAST(p.INDOCNO AS int) AS INDOCNO, p.CHAR_FIELD3, p.CHAR_FIELD7_AR, T.DESCRIPTION,J.DESCRIPTION AS [Section], p.SUBJECT
FROM dbo.TECHNICAL_MAIN p INNER JOIN
(SELECT MAX(revision_no) d, char_field1 c, char_field2_ar e, subcat_id j
FROM technical_main m
WHERE revision_no IN ('0', '1', '2')
GROUP BY char_field1, char_field2_ar, subcat_id) b
ON p.REVISION_NO = b.d AND p.CHAR_FIELD1 = b.c AND p.CHAR_FIELD2_AR = b.e AND p.REVISION_NO IN ('0', '1', '2')
INNER JOIN dbo.CUST_HIERARCHY_LOOKUP T ON p.CHAR_FIELD7_AR = T.ID
INNER JOIN dbo.CUST_HIERARCHY_LOOKUP J ON p.CHAR_FIELD3_AR = J.ID AND p.SUBCAT_ID = b.j

Good luck for all the folks