如何从一个表中选择行作为CSV并根据键插入另一个表？

Question

I have two tables testa and testb .

mysql> select * from testa;
+------+-------+
| id   | dcac  |
+------+-------+
|    1 | hello |
|    2 | world |
+------+-------+
2 rows in set (0.00 sec)

mysql> select * from testb;
+------+------+
| a_id | x    |
+------+------+
|    1 | a    |
|    1 | b    |
|    1 | b    |
|    1 | c    |
|    2 | x    |
+------+------+
5 rows in set (0.00 sec)

How do I add a column ( x_list ) to testa such that it's the comma-seperated list of x s from testb wherever testa.id is testb.a_id

So the output I'm expecting is somewhat like this -

+------+-------+--------+
| id   | dcac  | x-list |
+------+-------+--------+
|    1 | hello | a,b,b,c|
|    2 | world | x      |
+------+-------+--------+

I tried using some complex join statements and I looked at this http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat (did not really understand much)

But I'm not able to proceed. What do I do? Thanks.

Answer 1

Try:

SELECT testa.id, testa.dcac, GROUP_CONCAT(testb.x)
FROM testb
INNER JOIN testa ON testb.a_id = testa.id
GROUP BY testb.a_id

You can see result here: http://sqlfiddle.com/#!2/28887/2/0