Question

I’ve been pulling my hair out for two days trying to put a MySQL query together to pull some data together. This is beyond my level of experience with SQL, however.

The following query pulls the data that I need, but I need to format it differently so I can use it.

SELECT b.key, a.author, a.comment FROM action a, issue b 
WHERE a.issueid=b.id AND a.actiontype='comment';

This produces output like so:

1 | joe | comment 3
3 | sally | comment 2
1 | sam | comment 2
2 | julie | comment 2
1 | bill | comment 1
3 | joe | comment 1
2 | sam | comment 1

b.key is unique and can contain 0-∞ a.comment. There is a 1-1 relationship with the a.author and a.comment and I must maintain the original association. The output seems to be in ascending order based on the date of a.comment.

I would like to do get the data into the following format (CSV,) merging the a.author and a.comment results into a single column:

"1", "bill - comment 1", "sam - comment 2", "joe - comment 1"
"2", "julie - comment 1", "sam - comment 2"
"3", "joe - comment 1", "sally - comment 2"

I played around with several combinations of GROUP_CONCAT and ORDER and also messed with subqueries a bit based on this post and can’t seem to get it formatted the way I need. Additionally, it seems like the order of the comment column changes. I need to maintain the original (oldest to newest) order, but my original query above produces results in newest to oldest order. If the delimiters pose a problem, I can certainly do some post processing with perl or awk search & replace on the results. Any help is greatly appreciated!

Answer 1

How about

SELECT
    issue.key,
    GROUP_CONCAT(CONCAT(action.author, ' - ', action.comment) ORDER BY action.created ASC SEPARATOR '|')
FROM action
INNER JOIN issue
    ON action.issueid = issue.id
WHERE action.actiontype = 'comment'
GROUP BY issue.key;

with some post processing to split based on the pipe character. If you get truncation issues you may need to increase the value of group_concat_max_len.