SQL select with with multiple rows for one ID

Question

I have two tables:

Table 1: 'user_fields'

id  name
1   age
2   birthdate
3   firstname

Table 2: 'user_data'

user_id user_field_id value
22          1           50
22          2           01.01.1990
22          3           Peter
25          1           33
25          2           05.08.1970
25          3           Steve

Now I would like to create a sql statement which shows firstname and birthday for each user_id

example rows:

22    Peter    01.01.1990
25    Steve    05.08.1970

How should the select look like? Thanks a lot!

Answer 1

You'll need to join the tables (if you don't want to hardcode the values), and then perform an aggregation:

SELECT  ud.user_id,
        MIN(CASE WHEN uf.name = 'firstname' THEN ud.value END) as firstname,
        MIN(CASE WHEN uf.name = 'birthday' THEN ud.value END) as birthday
FROM user_data ud
INNER JOIN user_fields uf
    ON ud.user_field_id = uf.user_field_id 
GROUP BY ud.user_id;

Ok, per your new requirement, a simple JOIN will do:

SELECT  ud.user_id,
        MIN(CASE WHEN uf.name = 'firstname' THEN ud.value END) as firstname,
        MIN(CASE WHEN uf.name = 'birthday' THEN ud.value END) as birthday,
        MIN(ac.status) as status
FROM user_data ud
INNER JOIN user_fields uf
    ON ud.user_field_id = uf.user_field_id 
LEFT JOIN api_calls ac
    ON ud.user_id = ac.user_id
GROUP BY ud.user_id;