Question

I have table named comments:

ID | COMMENT | DATE     |
---|---------|----------|
1  | TEXT... | 01/01/12 |
2  | TEXT... | 01/01/12 |
3  | TEXT... | 15/01/12 |
4  | TEXT... | 01/01/13 |

In the table there are comments from 2012 and few from 2013. How can I select only records from 2012 and then get average comment count of 2012?

Answer 1

One really shouldn’t store temporal values in string-type columns. I suggest that you first convert your DATE column to MySQL’s DATE type:

ALTER TABLE comments ADD COLUMN new_date DATE AFTER `DATE`;
UPDATE comments SET new_date = STR_TO_DATE(`DATE`, '%d/%m/%y');
ALTER TABLE comments DROP COLUMN `DATE`;

(Obviously you will need to update your application code to use this new column).

Then:

1. How can I select only records from 2012

   You can simply use the inequality operators in a filter:

   SELECT *
   FROM  comments
   WHERE new_date BETWEEN '2012-01-01' AND '2013-01-01'
   

2. and then get average comment count of 2012?

   Not entirely sure what you mean by “average comment count”, but if you want the mean number of comments per day:

   SELECT COUNT(*) / DATEDIFF('2013-01-01', '2012-01-01')
   FROM   comments
   WHERE  new_date BETWEEN '2012-01-01' AND '2013-01-01'