Use GROUP_CONCAT in MySQL with considering null

Question

I have a table with 3 fields. This table keeps record of call duration for each day to the relevant country for last 30 days.

C_Date      Country         C_Time  
2012-10-01  India           1316
2012-10-01  USA             12  
2012-10-01  UK              132     
2012-10-01  Kuwait          134     
2012-10-02  UK              135     
2012-10-02  USA             136     
2012-10-02  Singapore       137     

I need to generate a table and a line graph using this records and I tried to write the MySQL query. Basically I need to draw this only for selected countries.
Say I want India, USA and UK ; then I need to pull a record set like this:

C_Date     | Calling_Time
-----------+----------------------------------
2012-10-01 | 1316,12,132
2012-10-02 | 0,136,135
2012-10-03 | ...
...        | ...

This is my Query:

SELECT C_Date, GROUP_CONCAT(C_Time
ORDER BY Country
SEPARATOR ',') as Calling_Time
FROM Call_Table t
WHERE Country
IN ('India', 'USA', 'UK')
GROUP BY C_Date
ORDER BY  C_Date

The result was much closer, but it had ignored the empty results.

C_Date     | Calling_Time
-----------+----------------------------------
2012-10-01 | 1316,12,132
2012-10-02 | 136,135   (expected 0,136,135)

Can I change my query to get the Calling_Time like 0,136,135 OR ,136,135 OR null,136,135 ?(with unique numbers of segments to represent each country )

Thanks in advance!

Answer 1

Try this query -

SELECT
  C_Date,
  CONCAT(MAX(IF(country = 'India', C_Time, 0)), ',',
         MAX(IF(country = 'USA', C_Time, 0)), ',',
         MAX(IF(country = 'UK', C_Time, 0))) Calling_Time
  FROM call_table
  GROUP BY C_Date

+------------+--------------+
| C_Date     | Calling_Time |
+------------+--------------+
| 2012-10-01 | 1316,12,132  |
| 2012-10-02 | 0,136,135    |
+------------+--------------+