How to pivot a table of strings in sql? [duplicate] - sql

Question

I'd like to pivot a table without using any PIVOT function but using pure SQL only (let's say PostgreSQL syntax for example).
So having this data-set as an example:
Order | Element | Value |
---------------------------
1 | Item | Bread |
1 | Quantity | 3 |
1 | TotalCost | 3,30 |
2 | Item | Pizza |
2 | Quantity | 2 |
2 | TotalCost | 10 |
3 | Item | Pasta |
3 | Quantity | 5 |
3 | TotalCost | 2,50 |
I'd expect to pivot on the Order column and having somenthing like:
Order | Item | Quantity | TotalCost |
-------------------------------------
1 | Bread | 3 | 3,30 |
2 | Pizza | 2 | 10 |
3 | Pasta | 5 | 2,50 |
How would I achieve that, once again, without using any pivot function?

Answer 1

Solution A
using CASE WHEN statements:
SELECT Order,
MAX(CASE WHEN Element = 'Item' THEN Value END) AS Item,
MAX(CASE WHEN Element = 'Quantity' THEN Value END) AS Quantity,
MAX(CASE WHEN Element = 'TotalCost' THEN Value END) AS TotalCost
FROM MyTable
GROUP BY 1
Solution B
Using self left joins:
SELECT A.Order, A.Item, B.Quantity, C.TotalCost
FROM
(SELECT Order, Value as Item
FROM MyTable
WHERE Element = 'Item') as A
LEFT JOIN
(SELECT Order, Value as Quantity
FROM MyTable
WHERE Element = 'Quantity') as B ON A.Order = B.Order
LEFT JOIN
(SELECT Order, Value as TotalCost
FROM MyTable
WHERE Element = 'TotalCost') as C ON B.Order = C.Order
The latter might not be as much as efficient but there are use case in which might come useful.

Answer 2

In Postgres, you would use FILTER:
SELECT Order,
MAX(Value) FILTER (WHERE Element = 'Item') AS Item,
MAX(Value) FILTER (WHERE Element = 'Quantity') AS Quantity,
MAX(Value) FILTER (WHERE Element = 'TotalCost') AS TotalCost
FROM MyTable
GROUP BY 1;
Note that ORDER is a SQL Keyword so it is a bad choice for a column name.