Q:

Mysql sales table grouped by customer and displayed by month columns pivot query

I have a sales table with the following columns:
|  Customer_Id | amount |  date  |

What would be the best way to group data by customer_id, and displaying  monthly total(SUM) of amount for each Customer_id (one row per Customer_id), on distinct month columns?
The desired output would be something like:
Customer     |January    | February   | March       | ....

Customer_id  |SUM amount | SUM amount | SUM amount | ....

I believe in Sql this is called a pivot table.
¡Thanks!

A:

Let's say you have following table:
mysql> select * from sales;
+-------------+--------+------------+
| customer_id | amount | date       |
+-------------+--------+------------+
|           1 |     12 | 2015-01-01 |
|           1 |      1 | 2015-01-02 |
|           1 |    663 | 2015-02-12 |
|           2 |     22 | 2015-01-03 |
|           2 |     21 | 2015-02-12 |
|           2 |     11 | 2015-02-12 |
|           2 |      9 | 2015-04-12 |
+-------------+--------+------------+

You can do this using this query:
SELECT
  customer_id,
  sum(if(month(date) = 1, amount, 0))  AS Jan,
  sum(if(month(date) = 2, amount, 0))  AS Feb,
  sum(if(month(date) = 3, amount, 0))  AS Mar,
  sum(if(month(date) = 4, amount, 0))  AS Apr,
  sum(if(month(date) = 5, amount, 0))  AS May,
  sum(if(month(date) = 6, amount, 0))  AS Jun,
  sum(if(month(date) = 7, amount, 0))  AS Jul,
  sum(if(month(date) = 8, amount, 0))  AS Aug,
  sum(if(month(date) = 9, amount, 0))  AS Sep,
  sum(if(month(date) = 10, amount, 0)) AS Oct,
  sum(if(month(date) = 11, amount, 0)) AS Nov,
  sum(if(month(date) = 12, amount, 0)) AS `Dec`
FROM sales
GROUP BY customer_id;

And the output:
+-------------+------+------+------+------+------+------+------+------+------+------+------+------+
| customer_id | Jan  | Feb  | Mar  | Apr  | May  | Jun  | Jul  | Aug  | Sep  | Oct  | Nov  | Dec  |
+-------------+------+------+------+------+------+------+------+------+------+------+------+------+
|           1 |   13 |  663 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |
|           2 |   22 |   32 |    0 |    9 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |    0 |
+-------------+------+------+------+------+------+------+------+------+------+------+------+------+

