generate index columns for "ORDER BY x, y" - mysql

Question

I use this query to summarize the contents of the table export_blocks, aggregated by user and date, and save it as a new table:
CREATE TABLE export_days
SELECT user_id DATE(submitted) AS date_str,
FROM export_blocks
GROUP BY user_id, DATE(submitted)
ORDER BY user_id, submitted
How can I, for each user_id get an incremental index for the date of records for that user? The indicies should start at 1 for each user, following the ORDER BY. I.e. I'd like to generate the date_index of the output below using SQL:
user_id date_str date_index
brian 2014-06-10 1
brian 2014-06-12 2
brian 2014-06-15 3
louis 2014-06-08 1
louis 2014-06-16 2
lucy 2013-11-15 1
(etc...)
I've been trying https://stackoverflow.com/a/5493480/1297830 but I cannot get it to work. It stops the counters prematurely, giving too low numbers for id_no and date_no.

Answer 1

Basing it on your sample query, you can do simple (dependent) subqueries to get the result;
SELECT id, date_str,
(SELECT COUNT(DISTINCT id)+1 FROM mytable WHERE id < a.id) id_no,
(SELECT COUNT(id)+1 FROM mytable WHERE id = a.id AND date_str < a.date_str) date_no
FROM mytable a
ORDER BY id;
...or you could do a couple of self joins;
SELECT a.id, a.date_str,
COUNT(DISTINCT b.id)+1 id_no,
COUNT(DISTINCT c.date_str)+1 date_no
FROM mytable a
LEFT JOIN mytable b ON a.id > b.id
LEFT JOIN mytable c ON a.id = c.id AND a.date_str > c.date_str
GROUP BY a.id, a.date_str
ORDER BY a.id, a.date_str;
An SQLfiddle showing both in action.
Sadly neither is really a very performant solution, but since MySQL lacks analytical (ie ranking) functions, the options are limited. Using user variables to do the ranking is also an option, however they're notoriously tricky to use and aren't portable so I'd go there only if performance demands it.

Answer 2

Based on Joachim's excellent answer I worked out the solution. It also works when there's multiple rows per day for each user.
CREATE TABLE export_days
SELECT
user_id, DATE(submitted) AS date_str,
(SELECT COUNT(DISTINCT DATE(submitted))+1 FROM export_blocks WHERE user_id = a.user_id AND submitted < a.submitted) date_no
FROM export_blocks a
GROUP BY user_id, DATE(submitted)
ORDER BY user_id, submitted