Using CASE to align values with user IDs - mysql

Question

I have a table which is a custom data table where name value pairs exist. Here's an example of some custom data in this table for an individual:
table custom_data
user_id | custom_data_name | custom_data_value
123 | initial contact date | 2014-01-01
123 | subscription start date | 2014-02-02
123 | favorite fruit | pears
I would like to create a query that parses this out at the individual level so I can see the data side by side like this:
user_id | initial_contact_date | subscription_start_date
123 | 2014-01-01 | 2014-02-02
I tried this:
SELECT
user_id,
CASE WHEN base1.custom_data_name = 'initial contact date' THEN custom_data.data END AS initial_contact_date,
CASE WHEN base1.custom_data_name = 'subscription start date' THEN custom_data.data END AS subscription_start_date
FROM
(
SELECT * FROM custom_data
WHERE custom_data_name = 'initial contact date' OR custom_data_name = 'subscription start date') base1
GROUP BY user_id
But I'm having a hard time interpreting the results. The results show, for each user, a value for EITHER initial_contact_date or subscription_start_date but not both together in one record.
How would I do that?

Answer 1

Try this:
SELECT
user_id,
MAX(CASE WHEN custom_data_name = 'initial contact date' THEN custom_data_value END) AS initial_contact_date,
MAX(CASE WHEN custom_data_name = 'subscription start date' THEN custom_data_value END) AS subscription_start_date
--MAX(CASE WHEN custom_data_name = 'favorite fruit' THEN custom_data_value END) AS favorite_fruit
FROM custom_data
GROUP BY user_id
Sample SQL Fiddle

Answer 2

You need to aggregate the data
select user_id
, min(case
when custom_data_name = 'initial contact date' then custom_data_value
end) initialContactDate
, min(case
when custom_data_name = 'subscription start date' then custom_data_value
end) subscriptionStartDate
from (
select '123' user_id, 'initial contact date' custom_data_name, '2014-01-01' custom_data_value union all
select '123' user_id, 'subscription start date' custom_data_name, '2014-01-02' custom_data_value union all
select '123' user_id, 'favorite fruit' custom_data_name, 'pears' custom_data_value
) tt
group by user_id
USER_ID INITIALCONTACTDATE SUBSCRIPTIONSTARTDATE
-----------------------------------------------------
123 2014-01-01 2014-01-02
SQLFiddle