Unpivot date columns to a single column of a complex query in Oracle - sql

Question

Hi guys, I am stuck with a stubborn problem which I am unable to solve. Am trying to compile a report wherein all the dates coming from different tables would need to come into a single date field in the report. Ofcourse, the max or the most recent date from all these date columns needs to be added to the single date column for the report. I have multiple users of multiple branches/courses for whom the report would be generated.
There are multiple blogs and the latest date w.r.t to the blogtitle needs to be grouped, i.e. max(date_value) from the six date columns should give the greatest or latest date for that blogtitle.
Expected Result:
select u.batch_uid as ext_person_key, u.user_id, cm.batch_uid as ext_crs_key, cm.crs_id, ir.role_id as
insti_role, (CASE when b.JOURNAL_IND = 'N' then
'BLOG' else 'JOURNAL' end) as item_type, gm.title as item_name, gm.disp_title as ITEM_DISP_NAME, be.blog_pk1 as be_blogPk1, bc.blog_entry_pk1 as bc_blog_entry_pk1,bc.pk1,
b.ENTRY_mod_DATE as b_ENTRY_mod_DATE ,b.CMT_mod_DATE as BlogCmtModDate, be.CMT_mod_DATE as be_cmnt_mod_Date,
b.UPDATE_DATE as BlogUpDate, be.UPDATE_DATE as be_UPDATE_DATE,
bc.creation_date as bc_creation_date,
be.CREATOR_USER_ID as be_CREATOR_USER_ID , bc.creator_user_id as bc_creator_user_id,
b.TITLE as BlogTitle, be.TITLE as be_TITLE,
be.DESCRIPTION as be_DESCRIPTION, bc.DESCRIPTION as bc_DESCRIPTION
FROM users u
INNER JOIN insti_roles ir on u.insti_roles_pk1 = ir.pk1
INNER JOIN crs_users cu ON u.pk1 = cu.users_pk1
INNER JOIN crs_mast cm on cu.crsmast_pk1 = cm.pk1
INNER JOIN blogs b on b.crsmast_pk1 = cm.pk1
INNER JOIN blog_entry be on b.pk1=be.blog_pk1 AND be.creator_user_id = cu.pk1
LEFT JOIN blog_CMT bc on be.pk1=bc.blog_entry_pk1 and bc.CREATOR_USER_ID=cu.pk1
JOIN gradeledger_mast gm ON gm.crsmast_pk1 = cm.pk1 and b.grade_handler = gm.linkId
WHERE cu.ROLE='S' AND BE.STATUS='2' AND B.ALLOW_GRADING='Y' AND u.row_status='0'
AND u.available_ind ='Y' and cm.row_status='0' and and u.batch_uid='userA_157'
I am getting a resultset for the above query with multiple date columns which I want > > to input into a single columnn. The dates have to be the most recent, i.e. max of the dates in the date columns.
I have successfully done the Unpivot by using a view to store the above
resultset and put all the dates in one column. However, I do not
want to use a view or a table to store the resultset and then do
Unipivot simply because I cannot keep creating views for every user
one would query for.
The max(date_value) from the date columns need to be put in one single column. They are as follows:
* 1) b.entry_mod_date, 2) b.cmt_mod_date ,3) be.cmt_mod_date , 4) b.update_Date ,5) be.update_date, 6) bc.creation_date *
Apologies that I could not provide the desc of all the tables and the
fields being used.
Any help to get the above mentioned max of the dates from these
multiple date columns into a single column without using a view or a
table would be greatly appreciated.*

Answer 1

It is not clear what results you want, but the easiest solution is to use greatest().
with t as (
YOURQUERYHERE
)
select t.*,
greatest(entry_mod_date, cmt_mod_date, cmt_mod_date, update_Date,
update_date, bc.creation_date
) as greatestdate
from t;

Answer 2

select <columns>,
case
when greatest (b_ENTRY_mod_DATE) >= greatest (BlogCmtModDate) and greatest(b_ENTRY_mod_DATE) >= greatest(BlogUpDate)
then greatest( b_ENTRY_mod_DATE )
--<same implementation to compare each time BlogCmtModDate and BlogUpDate separately to get the greatest then 'date'>
,<columns>
FROM table
<rest of the query>
UNION ALL
Select <columns>,
case
when greatest (be_cmnt_mod_Date) >= greatest (be_UPDATE_DATE)
then greatest( be_cmnt_mod_Date )
when greatest (be_UPDATE_DATE) >= greatest (be_cmnt_mod_Date)
then greatest( be_UPDATE_DATE )
,<columns>
FROM table
<rest of the query>
UNION ALL
Select <columns>,
GREATEST(bc_creation_date)
,<columns>
FROM table
<rest of the query>