How to combine SELECT DISTINCT and ROWNUM in Oracle Query - sql

Question

I need to combine the two MySQL statements below into a single ORACLE query if possible.
The initial query is
SELECT DISTINCT FIRST_NAME FROM PEOPLE WHERE LAST_NAME IN ("Smith","Jones","Gupta")
then based on each FIRST_NAME returned I query
SELECT *
FROM PEOPLE
WHERE FIRST_NAME = {FIRST_NAME}
AND LAST_NAME IN ("Smith","Jones","Gupta")
ORDER BY FIELD(LAST_NAME, "Smith","Jones","Gupta") DESC
LIMIT 1
The "List of last names" serves as a "default / override" indicator, so I only have one person for each first name, and where multiple rows for the same first name exist, only the Last match from the list of "Last Names" is used.
I need a SQL query that returns the last row from the "in" clause based on the order of the values in the IN(a,b,c). Here is a sample table, and the results I need from the query.
For the Table PEOPLE, with values
LAST_NAME FIRST_NAME
.....
Smith Mike
Smith Betty
Smith Jane
Jones Mike
Jones Sally
....
I need a query based on DISTINCT FIRST_NAME and LAST_NAME IN ('Smith','Jones') that returns
Betty Smith
Jane Smith
Mike Jones
Sally Jones

Answer 1

You can do it like this:
select first_name, last_name
from (
select p.first_name,
p.last_name,
row_number() over (partition by p.first_name
order by case p.last_name
when 'Smith' then 1
when 'Jones' then 2
when 'Gupta' then 3
end desc) as rn
from people p
where p.last_name in ('Smith','Jones','Gupta')
)
where rn = 1;
Demo: SQL Fiddle
EDIT
It's not hard to get more columns. I'm sure you could have figured it out with a bit more effort:
select *
from (
select p.*,
row_number() over (partition by p.first_name
order by case p.last_name
when 'Smith' then 1
when 'Jones' then 2
when 'Gupta' then 3
end desc) as rn
from people p
where p.last_name in ('Smith','Jones','Gupta')
)
where rn = 1;

Answer 2

Or like this:
select first_name,
max(last_name)
keep (dense_rank first order by decode(last_name,
'Smith', 1,
'Jones', 2,
'Gupta', 3) desc)
group by first_name
Oracle "FIRST"/"LAST" functions allow to get values from other columns of row with maximum/minimum value (for example get last_name of employee with maximum salary, or like in this case - get last_name from row with maximum rank)
http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions056.htm