MySQL dynamic pivot table - mysql

Question

Im trying to get a pivot table with dynamic columns to work. When user_id is a string, it works fine but if its an int, then it seems to fail
Here is what I have so far with the assistance of past questions:
CREATE TABLE measure2
(`inspection_date` date, `user_id` int, `score` int, comment text)
;
INSERT INTO measure2
(`inspection_date`, `user_id`, `score`, comment)
VALUES
('2012-10-16', 0, 0, null),
('2012-10-16', 1, 0, null),
('2012-10-16', 2, 0, null),
('2012-10-16', 3, 0, null),
('2012-10-17', 0, 1, null),
('2012-10-17', 1, 1, null),
('2012-10-17', 2, 1, null),
('2012-10-18', 3, 1, null)
;
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(case when user_id = ''',
user_id,
''' then score end) AS ',
user_id
)
) INTO #sql
FROM measure2;
SET #sql = CONCAT('SELECT inspection_date, ', #sql, '
FROM measure2
GROUP BY inspection_date');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
see: http://sqlfiddle.com/#!2/eab24/1
Im sure its something simple, but what am I missing?
Thanks

Answer 1

Since the values are in int you are are making them the column names, you have to wrap the values in a backtick
The sql will look like:
max(case when user_id = 1 then score end) as `1`
The full query will be:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(case when user_id = ''',
user_id,
''' then score end) AS `',
user_id, '`'
)
) INTO #sql
FROM measure2;
SET #sql = CONCAT('SELECT inspection_date, ', #sql, '
FROM measure2
GROUP BY inspection_date');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
See SQL Fiddle with Demo

Answer 2

Simple indeed - numbers alone aren't valid column names in SQL, so you need to amend your code to enclose them in backticks:
SET #sql = NULL;
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'max(case when user_id = ',
user_id,
' then score end) AS `',
user_id,
'`'
)
) INTO #sql
FROM measure2;
SET #sql = CONCAT('SELECT inspection_date, ', #sql, '
FROM measure2
GROUP BY inspection_date');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
I suggest retaining this change for string values as well, in case some of your string values match reserved words or include spaces.
(Also, ' aren't required around numeric values, so I have removed them from the case clauses.)
SQLFiddle here.