I have a table like below
user_id | month, | value
---------+------------+--------
1 | 2013-02-01 | 1
1 | 2013-01-01 | 0
1 | 2013-03-01 | 5
2 | 2013-02-01 | 1
Supposedly a user_id
can not have same month
more than one.
Let's say I can put the months I want to query in the query statement. like below
SELECT user_id, (bla bla bla) AS '2013-03-01', (bla bla bla) AS '2013-02-01'
How do I get a result like below, with minimum number of queries and post-processing (eg using python or php)?
user_id | 2013-03-01 | 2013-02-01 | 2013-01-01
---------+------------+------------+------------
1 | 5 | 1 | 0
2 | NULL | 1 | NULL
You can use conditional aggregates to get the required result set:
SELECT user_id,
MAX(CASE WHEN month = '2013-03-01' THEN value END) AS '2013-03-01',
MAX(CASE WHEN month = '2013-02-01' THEN value END) AS '2013-02-01',
MAX(CASE WHEN month = '2013-01-01' THEN value END) AS '2013-01-01'
FROM mytable
GROUP BY user_id
This works as long there is a predefined set of month
values. Otherwise you have to use dynamic SQL.
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