Finding columns with highest value among other columns in SQL - sql

Question

I have a table that looks like this:
table,
th,
td {
border: 1px solid black;
<table>
<tr>
<th>Customer</th>
<th>Category 1</th>
<th>Category 2</th>
<th>Category 3</th>
<th>Category 4</th>
</tr>
<tr>
<td>aaaaa#aaa.com</td>
<td>0</td>
<td>563</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>bbbb#bbb.com</td>
<td>33</td>
<td>31</td>
<td>38</td>
<td>13</td>
</tr>
<tr>
<td>cccc#ccc.com</td>
<td>108</td>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr>
<td>dddd#ddd.com</td>
<td>0</td>
<td>7</td>
<td>0</td>
<td>11</td>
</tr>
</table>
I am trying to insert a new column named "BestCategory" that will show the name of the category that has the highest value in between them.
I have tried to use GREATEST but it's not accepted in my system.
Can you guys help me?

Answer 1

First you have to use UNPIVOT to calculate the maxValue for each row
Then use a CASE to select what is the BestCategory.
Sql Fiddle Demo
WITH maxValues as
(
select
[Customer], Max(Amount) as TheMax
from
Customer
UNPIVOT (Amount for AmountCol in
([Category 1], [Category 2], [Category 3], [Category 4])) as unpvt
group by [Customer]
)
select
Customer.[Customer], [Category 1], [Category 2], [Category 3], [Category 4],
TheMax,
Case
WHEN [Category 1] = TheMax THEN '[Category 1]'
WHEN [Category 2] = TheMax THEN '[Category 2]'
WHEN [Category 3] = TheMax THEN '[Category 3]'
ELSE '[Category 4]'
END as BestCategory
from Customer
inner join maxValues
on Customer.[Customer] = maxValues.[Customer]
OUTPUT
| Customer | Category 1 | Category 2 | Category 3 | Category 4 | TheMax | BestCategory |
|---------------|------------|------------|------------|------------|--------|--------------|
| aaaaa#aaa.com | 0 | 563 | 0 | 0 | 563 | [Category 2] |
| bbbb#bbb.com | 33 | 31 | 38 | 13 | 38 | [Category 3] |
| cccc#ccc.com | 108 | 0 | 0 | 0 | 108 | [Category 1] |
| dddd#ddd.com | 0 | 7 | 0 | 11 | 11 | [Category 4] |

Answer 2

If you want the columnname in the "greatest field" you could use the idea in this sqlfiddle example
It selects the columnname with the greatest value per row
SELECT CASE
WHEN [category 1] > [category 2]
AND [category 1] > [category 3]
AND [category 1] > [category 4]
THEN '[Category 1]'
ELSE CASE
WHEN [category 2] > [category 1]
AND [category 2] > [category 3]
AND [category 2] > [category 4]
THEN '[Category 2]'
ELSE CASE
WHEN [category 3] > [category 1]
AND [category 3] > [category 2]
AND [category 3] > [category 4]
THEN '[Category 3]'
ELSE '[category 4]'
END
END
END
FROM customer