Converting column into row using "|" as separators - mysql

Question

Please take a look at this Fiddle Example
I want to convert each field into a row from this table:
CREATE TABLE product
(`ID` int, `name` varchar(1), `category` varchar(11), `price` int,`year`int)
;
INSERT INTO product
(`ID`, `name`, `category`, `price`,`year`)
VALUES
(1, 'A', 'Outdoor', 25,2010),
(2, 'A', 'Doll', 34,2009),
(3, 'C', 'Doll', 25,2008),
(4, 'D', 'Outdoor', 20,2010),
(5, 'E', 'Brainteaser', 22,2010),
(6, 'E', 'Brainteaser', 22,2009),
(7, 'G', 'Brainteaser', 30,2009),
(8, 'G', 'Brainteaser', 30,2009)
;
Here's the output I'm trying to get:
field value
name A,C,D,E,G
category Brainteaser,Doll,Outdoor
price 20,22,25,30,34
year 2008,2009,2010
I read a thread about pivoting table with UNION and MAX but I was lost at using MAX with GROUP_CONCAT
SELECT
MAX(CASE WHEN ... GROUP_CONCAT(DISTINCT (value) SEPARATOR '|')) as value
from(
select id,name value, 'name' field
from product
union all
select id,category value, 'category' field
from product
union all
select id,price value, 'price' field
from product
union all
select id,year value, 'year' field
from product
)
GROUP BY field
order by value
Can anyone show me how to get that output?

Answer 1

This will give you expected output:
SELECT 'name' AS `field`. GROUP_CONCAT(DISTINCT `name` ORDER BY `name`) AS `value`
FROM product
UNION ALL
SELECT 'category' AS `field`. GROUP_CONCAT(DISTINCT `category` ORDER BY `category`) AS `value`
FROM product
UNION ALL
SELECT 'price' AS `field`. GROUP_CONCAT(DISTINCT `price` ORDER BY `price`) AS `value`
FROM product
UNION ALL
SELECT 'year' AS `field`. GROUP_CONCAT(DISTINCT `year` ORDER BY `year`) AS `value`
FROM product
Added ORDER BY because looks like you need sorted output

Answer 2

something like this?? Using union all for better proformance and incase there are any dupilcates.
SELECT 'name' field, group_concat(DISTINCT name ORDER BY name SEPARATOR '|') value FROM product
UNION ALL
SELECT 'category' field, group_concat(DISTINCT category ORDER BY category SEPARATOR '|') value FROM product
UNION ALL
SELECT 'price' field, group_concat(DISTINCT price ORDER BY price SEPARATOR '|') value FROM product
UNION ALL
SELECT 'year' field, group_concat(DISTINCT year ORDER BY year SEPARATOR '|') value FROM product;
EDIT:
If you would like to do this with just one query you can achieve it this way.
SELECT
#uName := group_concat(DISTINCT name ORDER BY name SEPARATOR '|'),
#uCat := group_concat(DISTINCT category ORDER BY category SEPARATOR '|') uCat,
#uPrice := group_concat(DISTINCT price ORDER BY price SEPARATOR '|') uPrice,
#uYear := group_concat(DISTINCT year ORDER BY year SEPARATOR '|') uYear
FROM product;
SELECT 'name' field, #uName value
UNION ALL
SELECT 'category' field, #uCat value
UNION ALL
SELECT 'price' field, #uPrice value
UNION ALL
SELECT 'year' field, #uYear value;
NOTE: you can do ORDER BY inside the GROUP_CONCAT

Answer 3

There is a way to complete your request without having to query your table with many queries. In fact, method below is a way to turn any table to pivot. It will use mysql prepared statements for prepare SQL and later execute it:
SELECT
GROUP_CONCAT(f SEPARATOR ' UNION ALL ')
FROM
(SELECT
CONCAT(
'SELECT "',
column_name,
'" AS `field`, GROUP_CONCAT(DISTINCT ',
column_name,
') AS `value` FROM `',
#table_name,
'`'
) AS f
FROM
((SELECT
column_name
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
table_name=#table_name &&
table_schema=#schema_name
) AS fields
CROSS JOIN
(SELECT
#table_name := 'product',
#schema_name:= 'test'
) AS init)
) AS sqldata
The sql above will result in a string, which can be used to assign a variable, like
mysql> SET #sql:=(SELECT GROUP_CONCAT(f SEPARATOR ' UNION ALL ') FROM (SELECT CONCAT('SELECT "', column_name,'" AS `field`, GROUP_CONCAT(DISTINCT ', column_name,') AS `value` FROM `', #table_name, '`') AS f FROM ((SELECT column_name FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name=#table_name && table_schema=#schema_name) AS fields CROSS JOIN (SELECT #table_name:='product', #schema_name:='test') AS init)) AS sqldata);
Query OK, 0 rows affected (0.03 sec)
next, prepare:
mysql> PREPARE stmt FROM #sql;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
finally, execute it:
mysql> EXECUTE stmt;
+----------+--------------------------+
| field | value |
+----------+--------------------------+
| ID | 1,2,3,4,5,6,7,8 |
| name | A,C,D,E,G |
| category | Outdoor,Doll,Brainteaser |
| price | 25,34,20,22,30 |
| year | 2010,2009,2008 |
+----------+--------------------------+
5 rows in set (0.00 sec)
The benefit is that you are independent from table structure, field names, e tc. It's a general way - so you may use it to create such pivots for any table.
Few words about variables #table_name and #schema_name. They specify which table and in which schema would be pivoted. In sample above, I used CROSS JOIN to set them in-place, but you may set them separately, to maintain different tables for pivots.