根据列条件从2个值中选择包含多行的第一个值，否则从所有行选择第二个值ORACLE

Question

i have below oracle sql

select     *      from     a
where     a.description      in 
('Rebook All (1)', 'Created stock identifier') 
and     a.date     between     '03/18/2017 00:00:01' 
AND     '03/25/2017 00:00:00'
and     a.unit     =     '38240007294677' 

Now result can have both description like below for a Unit number or can have 1 of the description , when it has both description for a Unit number i need to select only 'Rebook all (1)'(this description can be there many times as shows below in results) description not 'Created stock identifier' and its related details from table a and when it has only 1 description out of these 2 then if 'Rebook All (1)' not there select 'Created stock identifier' and vice versa. how do i select it? Thanks in advance.

Date                       Description

3/20/2017 10:11:12.769000 AM Created stock identifier

3/20/2017 10:10:47.775000 AM Created stock identifier

3/20/2017 10:10:47.782000 AM Created stock identifier

3/20/2017 8:14:41.696000 PM Rebook all (1)

3/20/2017 8:14:41.885000 PM Rebook all (1)

3/20/2017 8:13:51.622000 PM Rebook all (1)

Answer 1

One method uses rank() :

select a.*
from (select a.*,
             rank() over (partition by unit order by description desc) as seqnum
      from a
      where a.description in  ('Rebook All (1)', 'Created stock identifier') 
            a.date >= date '2017-03-18' and
            a.date < date '2017-03-25' and
            a.unit = '38240007294677' 
    ) a
where seqnum = 1;

Notes: - This uses the fact that "Rebook" comes alphabetically after "Created". Hence the desc in the order by . - I prefer ANSI standard date formats. - Notice the change to the date logic, to eliminate the need for times on the dates.