Oracle: Get column names of Top n values over multiple columns - oracle

Question

My question is similar to
https://community.oracle.com/message/4418327
in my query i need the MAX value of 3 different columns.
example: column 1 = 10, column 2 = 20, column 3 = 30 > output should
be 30. i need this MAX value to sort the list by it.
However instead of the actually value I need the column name and ideally not just the max one but top 3 as example.
The desired output would then be
ID first second third
-------------------------------
1 column 3 column 2 column1

Answer 1

There is no built-in function for what you are asking. So user1578653's answer is good, straight-forward and fast. Another way would be to write a function with PL/SQL.
In case you want to use pure SQL, but want it easier to add columns to the comparision, then if you are satisfied with just two columns (id and column names string), you can do this:
select id, listagg(colname, ', ') within group (order by value desc) as columns
from
(
select id, 'column1' as colname, col1 as value from mytable
union all
select id, 'column2' as colname, col2 as value from mytable
union all
select id, 'column3' as colname, col3 as value from mytable
-- add more columns here, if you wish
)
group by id;
Be aware this is slower than user1578653's SQL statement, as the table is being read three times. (I also treat equal values differently here, same values lead to random order.)

Answer 2

You can use PIVOT/UNPIVOT for this.
Fisrt UNPIVOT your table and assign rank with values ordered in descending order.
create table sample(
id number,
col1 number,
col2 number,
col3 number
);
insert into sample values(1,10,20,30);
insert into sample values(2,10,20,15);
select id, col_name, val,
row_number() over (partition by id order by val desc) r
from sample
unpivot(val for col_name in (
col1 AS 'col1', col2 AS 'col2', col3 AS 'col3')
);
Output:
| ID | COL_NAME | VAL | R |
|----|----------|-----|---|
| 1 | col3 | 30 | 1 |
| 1 | col2 | 20 | 2 |
| 1 | col1 | 10 | 3 |
| 2 | col2 | 20 | 1 |
| 2 | col3 | 15 | 2 |
| 2 | col1 | 10 | 3 |
sqlfiddle.
Next PIVOT the col_name based on the rank column.
with x(id, col_name, val,r) as (
select id, col_name, val,
row_number() over (partition by id order by val desc)
from sample
unpivot(val for col_name in (
col1 AS 'col1', col2 AS 'col2', col3 AS 'col3')
)
)
select * from (
select id, col_name, r
from x
)
pivot(max(col_name) for r in (
1 as first, 2 as second, 3 as third)
);
Output:
| ID | FIRST | SECOND | THIRD |
|----|-------|--------|-------|
| 1 | col3 | col2 | col1 |
| 2 | col2 | col3 | col1 |
sqlfiddle.

Answer 3

Not sure if there is a better way of doing this, but here's a possible solution using the CASE statement. Here's the table structure I've tested it on:
CREATE TABLE MAX_COL(
"ID" INT,
COLUMN_1 INT,
COLUMN_2 INT,
COLUMN_3 INT
);
And here's the SQL I used:
SELECT
"ID",
CASE
WHEN COLUMN_1 > COLUMN_2 AND COLUMN_1 > COLUMN_3 THEN 'COLUMN_1'
WHEN COLUMN_2 > COLUMN_1 AND COLUMN_2 > COLUMN_3 THEN 'COLUMN_2'
WHEN COLUMN_3 > COLUMN_2 AND COLUMN_3 > COLUMN_1 THEN 'COLUMN_3'
ELSE 'NONE'
END AS "FIRST",
CASE
WHEN COLUMN_1 > COLUMN_2 AND COLUMN_1 < COLUMN_3 THEN 'COLUMN_1'
WHEN COLUMN_2 > COLUMN_1 AND COLUMN_2 < COLUMN_3 THEN 'COLUMN_2'
WHEN COLUMN_3 > COLUMN_2 AND COLUMN_3 < COLUMN_1 THEN 'COLUMN_3'
ELSE 'NONE'
END AS "SECOND",
CASE
WHEN COLUMN_1 < COLUMN_2 AND COLUMN_1 < COLUMN_3 THEN 'COLUMN_1'
WHEN COLUMN_2 < COLUMN_1 AND COLUMN_2 < COLUMN_3 THEN 'COLUMN_2'
WHEN COLUMN_3 < COLUMN_2 AND COLUMN_3 < COLUMN_1 THEN 'COLUMN_3'
ELSE 'NONE'
END AS "THIRD"
FROM
MAX_COL;
Please note that you will need to deal with situations where one or more columns have the same value. In this case I am just returning 'NONE' if this occurs, but you may want to do something else.
UPDATE
You could also use PLSQL functions to achieve this, which may be easier to use for many columns. Here's an example:
CREATE OR REPLACE
FUNCTION COLUMN_POSITION (IDVAL INT, POSITION INT) RETURN VARCHAR2 AS
TYPE COLUMN_VALUE_TYPE IS TABLE OF NUMBER INDEX BY VARCHAR2(64);
COLS COLUMN_VALUE_TYPE;
COL_KEY VARCHAR2(64);
QUERY_STR VARCHAR2(1000 CHAR) := 'SELECT COL FROM(SELECT T.*, DENSE_RANK() OVER (ORDER BY VAL DESC) AS RANK FROM (';
COL_NAME VARCHAR2(64);
BEGIN
COLS('COLUMN_1') := NULL;
COLS('COLUMN_2') := NULL;
COLS('COLUMN_3') := NULL;
--ADD MORE COLUMN NAMES HERE...
COL_KEY := COLS.FIRST;
LOOP
EXIT WHEN COL_KEY IS NULL;
QUERY_STR := QUERY_STR || 'SELECT ' || COL_KEY || ' AS VAL, '''|| COL_KEY ||''' AS COL FROM MAX_COL WHERE ID = '|| IDVAL ||' UNION ALL ';
COL_KEY := COLS.NEXT(COL_KEY);
END LOOP;
QUERY_STR := SUBSTR(QUERY_STR, 0, LENGTH(QUERY_STR) - 11);
QUERY_STR := QUERY_STR || ') T ) WHERE RANK = ' || POSITION;
EXECUTE IMMEDIATE QUERY_STR INTO COL_NAME;
RETURN COL_NAME;
END;
This example has only 3 columns but you could easily add more. You can then use this in a query like this:
SELECT
MAX_COL.*,
COLUMN_POSITION(ID, 1) AS "FIRST",
COLUMN_POSITION(ID, 2) AS "SECOND",
COLUMN_POSITION(ID, 3) AS "THIRD"
FROM MAX_COL

Answer 4

SELECT
(CASE
WHEN A > B AND A > C THEN 'A'
WHEN B > A AND B > C THEN 'B'
WHEN C > B AND C > A THEN 'C'
END) AS "MaxValue_Column_Name",
greatest(A,B,C) AS Max_Value FROM max_search ;
--table name =max_search and column_name are A,B and C