Getting 2nd Least Value from Different Column

Question

Hi there All,
I have one odd requirement.
I hava table which has diffrent columns of numeric Datatype.
The task is to get the least values from the table.
I can take the least value by least(col1,col2,col3 ...) function.Until this stage it is fine.
But also I have take 2nd least value and 3rd least value, which I am quite unsure how to get it.
Looking forward for suggestions.
Thanks in Advance.
Regards,
Ajeet

Answer 1

The following is a generic solution that will allow you to select the nth least and allow you to pass as many column names as you like and will return null if the nth least requested exceeds the number of distinct values. The nleast function that I wrote uses the str2tbl function by Tom Kyte. I have included a demonstration of its usage below. The value returned for the 1st least is the same as that returned by the least function.
This should have been posted on the SQL and PL/SQL discussion group of these forums, rather than the general database. I also posted the same response in the SQL discussion group of the Orafaq forums.
scott@ORA92> -- test data:
scott@ORA92> SELECT * FROM your_table
  2  /
      COL1       COL2       COL3
         1          2          3
         4          6          5
         8          7          9
        11         12         10
        15         13         14
        18         17         16
6 rows selected.
scott@ORA92> -- type and functions:
scott@ORA92> create or replace type myTableType as table of number;
  2  /
Type created.
scott@ORA92> create or replace function str2tbl( p_str in varchar2 )
  2  return myTableType
  3  as
  4        l_str      long default p_str || ',';
  5        l_n         number;
  6        l_data    myTableType := myTabletype();
  7  begin
  8        loop
  9            l_n := instr( l_str, ',' );
10            exit when (nvl(l_n,0) = 0);
11            l_data.extend;
12            l_data( l_data.count ) := ltrim(rtrim(substr(l_str,1,l_n-1)));
13            l_str := substr( l_str, l_n+1 );
14        end loop;
15        return l_data;
16  end;
17  /
Function created.
scott@ORA92> CREATE OR REPLACE FUNCTION nleast
  2    (p_n        IN NUMBER,
  3       p_nums        IN VARCHAR2)
  4    RETURN           NUMBER
  5  AS
  6    v_nleast      NUMBER;
  7  BEGIN
  8    SELECT DISTINCT column_value
  9    INTO   v_nleast
10    FROM   (SELECT column_value,
11                  DENSE_RANK () OVER (ORDER BY column_value) AS num_rk
12              FROM   (select *
13                   from   table (CAST (str2tbl (p_nums) AS mytabletype)))
14             WHERE   column_value IS NOT NULL)
15    WHERE  num_rk = p_n;
16    RETURN v_nleast;
17  EXCEPTION
18    WHEN OTHERS THEN RETURN NULL;
19  END nleast;
20  /
Function created.
scott@ORA92> SHOW ERRORS
No errors.
scott@ORA92> -- query:
scott@ORA92> SELECT col1, col2, col3,
  2           LEAST (col1, col2, col3) AS the_least,
  3           nleast (1, col1 || ',' || col2 || ',' || col3) AS first_least,
  4           nleast (2, col1 || ',' || col2 || ',' || col3) AS second_least,
  5           nleast (3, col1 || ',' || col2 || ',' || col3) AS third_least,
  6           nleast (4, col1 || ',' || col2 || ',' || col3) AS fourth_least
  7  FROM   your_table
  8  /
      COL1       COL2       COL3  THE_LEAST FIRST_LEAST SECOND_LEAST THIRD_LEAST FOURTH_LEAST
         1          2          3          1           1            2           3
         4          6          5          4           4            5           6
         8          7          9          7           7            8           9
        11         12         10         10          10           11          12
        15         13         14         13          13           14          15
        18         17         16         16          16           17          18
6 rows selected.