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  1. Prepare
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  3. Aggregation
  4. Weather Observation Station 15
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Weather Observation Station 15

  • lelcat
     + 1 comment

    Using Oracle...
    Most of the answers listed in this discussion have answers like this:

    // Solution1 -- order by desc and select top
select * from 
  (select round(LONG_W,4) from STATION
    where LAT_N<137.2345
    order by LAT_N desc) 
 where rownum=1;

    Is there anything worse about this pattern? I would have thought ordering was more resource intensive than assigning a variable and seeking. Is there a reason not to do this?

    // Solution 2 -- assign max_lat_n variable and seek
variable max_lat_n number;
exec select max(LAT_N) into :max_lat_n from STATION where LAT_N<137.2345;
select round(LONG_W,4) from STATION where LAT_N=:max_lat_n;


    And does this subquery approach repeat the max() operation on every row?

    // Solution 3 -- subquery the max() operation
select round(LONG_W,4) from STATION
  where LAT_N=(select max(LAT_N) from STATION
                 where LAT_N<137.2345);