MySQL pivot query

问题:

I used to have a query

SELECT ps_target_ecpm, ps_actual_ecpm FROM publisher_stats JOIN domain ON domain.dmn_id = ps_dmn_id LEFT JOIN langue ON langue.lng_id = domain.default_lng_id WHERE MONTH(ps_month) = 05  

The result I need should look like

may_target_ecmp, may_actual_ecpm, april_target_ecpm, april_actual_ecpm, march_target_ecpm, march_actual_ecpm.

For april MONTH(ps_month) = 04 and for march MONTH(ps_month) = 03 respectively.

After some questioning around I ended up with a query that looks like this

SELECT (CASE WHEN MONTH(ps_month) = 4 THEN ps_target_ecpm ELSE 0 END) AS april_target_ecpm,  (CASE WHEN MONTH(ps_month) = 4 THEN ps_actual_ecpm ELSE 0 END) AS april_actual_ecpm, (CASE WHEN MONTH(ps_month) = 3 THEN ps_target_ecpm ELSE 0 END) AS march_target_ecpm,  (CASE WHEN MONTH(ps_month) = 3 THEN ps_actual_ecpm ELSE 0 END) AS march_actual_ecpm  FROM publisher_stats JOIN domain ON domain.dmn_id = ps_dmn_id LEFT JOIN langue ON langue.lng_id = domain.default_lng_id 

The resultset I get is not quite what I need. The example response is:

0           0       0.48    0.27 0.48        0.47    0       0 

While I need it to be in one row

0.48    0.47    0.48    0.27 

Could you please help me to figure out how to make this query do what it is intended to. Thanks in advance

P.S. This question come all the way from this question - mysql pivoting - how can I fetch data from the same table into different columns?

回答1:

Just use an aggregate function, MAX for example will work fine, but you might need to use SUM if you need to get the total for each month, if there are multiple entries for ps_target_ecpm for each month. Like this:

SELECT   MAX(CASE WHEN MONTH(ps_month) = 4 THEN ps_target_ecpm ELSE 0 END) AS april_target_ecpm,    MAX(CASE WHEN MONTH(ps_month) = 4 THEN ps_actual_ecpm ELSE 0 END) AS april_actual_ecpm,   MAX(CASE WHEN MONTH(ps_month) = 3 THEN ps_target_ecpm ELSE 0 END) AS march_target_ecpm,    MAX(CASE WHEN MONTH(ps_month) = 3 THEN ps_actual_ecpm ELSE 0 END) AS march_actual_ecpm  FROM publisher_stats JOIN domain ON domain.dmn_id = ps_dmn_id LEFT JOIN langue ON langue.lng_id = domain.default_lng_id 

文章来源: MySQL pivot query