选择MAX时不是单组组功能

Question

Select sg_gameno, Max(sg_Year), sg_end, sg_hostcity, country_olympic_name
  from Summergames s, Country co
 where s.country_isocode = co.country_isocode 

Don't know whats wrong with this. I want to get the lastest year. Should i use MAX or something else.

Answer 1

In Oracle, you can't have aggregate functions and individual columns in the SELECT list, unless the individual columns are included in GROUP BY clause.

You can use RANK or DENSE_RANK function to rank the records based on thet year and then select the from the resultset the top ranked rows.

select * from (
    select sg_gameno, sg_Year, sg_end, sg_hostcity, country_olympic_name,
           rank() over (order by sg_year desc) as ranking
      from Summergames s, Country co
     where s.country_isocode = co.country_isocode
     )
  where ranking = 1;

You can also use following query to get the same result. You will have to select the one that performs best for you.

select sg_gameno, sg_Year, sg_end, sg_hostcity, country_olympic_name
  from Summergames s, Country co
 where s.country_isocode = co.country_isocode
   and sg_Year = (select max(sg_Year)
                    from Summergames s, Country co
                   where s.country_isocode = co.country_isocode);

Answer 2

If you want to aggregate one column ( sg_year ) and to not aggregate others, you need a GROUP BY clause.

Select sg_gameno, Max(sg_Year), sg_end, sg_hostcity, country_olympic_name
  from Summergames s, 
       Country co
 where s.country_isocode = co.country_isocode 
 group by sg_gameno, sg_end, sg_hostcity, country_olympic_name

is syntactically valid. Whether it provides you the results you want is another question-- you'd need to tell us what your tables look like, what data is in them, what result you want, etc.