Wordpress - Get Post Number in a Category

Is there a way for me to get a pseudo-ID of a post from the category it belongs to? Let's say I have these posts

post_id | post_title | post_cat
--------+------------+---------
0       | a post     | cat1
1       | a post1    | cat2
2       | a post2    | cat1
3       | a post3    | cat2
...
57      | a post57   | cat2

I want the posts from cat2 and the posts' ids to be relative to the category they were posted in. Something like

post_id | post_title | post_cat | cat_post_id
--------+------------+----------+--------
1       | a post1    |开发者_如何学JAVA cat2     | 1
3       | a post3    | cat2     | 2
57      | a post57   | cat2     | 3

Are you trying to achieve something similar to what we have discussed here - Creating a numerical order index on a MySQL table

SET @rank=0;
SELECT @rank:=@rank+1 AS cat_post_id, post_id, post_title, post_cat
FROM posts
WHERE post_cat = 'cat2'
ORDER BY post_id DESC;

is this in the loop? If it is:

if(is_category(2)) {
     echo the_ID();
     i++;
     echo i++;
}

Now if you are doing this through SQL. You will have to add a column.