mysql - Select the 3 smallest values from multiple columns - mysql

Question

ID COL1 COL2 COL3 COL4 COL5 COL6 COL7
-------------------------------------
1 4 13 8 0 9 11 2
2 12 3 3 10 17 12 9
3 17 0 0 19 3 1 3
4 5 0 16 0 9 11 2
Here is an example table of data.
What I need to be able to do is to select and label the three smallest values in each row so I can identify each one.
For instance I want to know that in Row2 the three smallest values are 3,3,9 and that they are in COL2,COL3,COL7
I am thinking that I need to incorporate the LEAST() command provided in mysql but it only seems to return one value (the smallest one).
SELECT LEAST(COL1,COL2,COL3,COL4,COL5,COL6,COL7)
I cant seem to figure out how to get the 3 smallest values instead of just one.

Answer 1

Unfortunately your table is not normalized :(
In this case a possible solution is to unpivot the table using a query like this:
CREATE VIEW unpivoted AS
SELECT id, 'col1' colname, col1 as value FROM Table1
UNION ALL
SELECT id, 'col2' colname, col2 FROM Table1
UNION ALL
SELECT id, 'col3' colname, col3 FROM Table1
UNION ALL
SELECT id, 'col4' colname, col4 FROM Table1
UNION ALL
SELECT id, 'col5' colname, col5 FROM Table1
UNION ALL
SELECT id, 'col6' colname, col6 FROM Table1
UNION ALL
SELECT id, 'col7' colname, col7 FROM Table1
and then use a query like the below to find 3 minimum values and then pivot results back:
SET #x = 0;
Set #lastid = -999;
SELECT id,
min( IF( x = 0, colname, null )) As Colname1,
min( IF( x = 0, value, null )) As value1,
min( IF( x = 1, colname, null )) As Colname2,
min( IF( x = 1, value, null )) As value2,
min( IF( x = 2, colname, null )) As Colname3,
min( IF( x = 2, value, null )) As value3
FROM (
SELECT id, colname, value,
IF( #lastid = id, #x:=#x+1,
IF( (#lastid:=id), #x:=0, #x:=0 )
) As x
FROM unpivoted
ORDER BY id, value
) q
WHERE x < 3
GROUP BY id
Demo: http://sqlfiddle.com/#!2/f20ee4/5
But the speed of these queries will be horribly slow, don't even try them on a big table.
You need to normalize the table.

Answer 2

Kordirko's solution is may be the fastest way to do it (without a whole lot of comparison logic on each row). However, the following is more intuitive, in my opinion:
select id,
substring_index(group_concat(colname order by value), ',', 3) as Top3Columns,
substring_index(group_concat(value order by value), ',', 3) as Top3Values
from unpivoted
group by id;
This puts the names and values each in one column, as a concatenated list. You can use a similar idea if you want them in separate columns.