=====Description=====
This table stores companys' performance by month. 
Abouts 239402 records（2014-01-21）.

=====Table format=====
^ Field    ^Type       ^Null ^ Key ^Default ^ Extra |
| stock_id | bigint(20) | NO   | PRI | NULL    |       |
| date     | double     | NO   | PRI | NULL    |       |
| mth_ret  | double     | NO   |     | NULL    |       |


=====record example=====
^ stock_id ^date   ^ mth_ret   ^
|        1 | 199201 |  0.010984 |
|        1 | 199202 | -0.024365 |

=====change log=====
newly built
<code>
CREATE TABLE `stock_return` (
  `stock_id` bigint(20) NOT NULL,
  `date` double NOT NULL,
  `mth_ret` double NOT NULL,
  PRIMARY KEY (`stock_id`,`date`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
</code>