MySQL Join two tables and combine multiple rows into one - mysql

Question

I have 2 tables:
sms_recipients
campaign_id | message | user_id | contact_number | status
.........................................................
1 something 12334 078237812719 1
1 something 12123 071231231232 1
2 other 12124 078123123126 0
2 other 12334 078234234212 0
2 other 42124 078124124415 1
sms_campaign
campaign_id | shop_id| campaign_type
.....................................
1 1123 marketing
2 2123 awareness
3 3231 something else
4 4432 bla bla
5 5244 last
campaign_id's are unique for the sms_campaign table, there are multiple user_id's related to the same campaign_id the message is the same for all unique champagne_id
I want to combine them so that every contact_number of the same campaign_id with a status = 0 appears in a single row and column like this:
campaign_id | shop_id| campaign_type | users_mobile_numbers | message
..........................................................................
1 1123 marketing something
2 2123 awareness 078123123126,078234234212 other
3 3231 something else
4 4432 078234234212
5 5244 078124124415
Here is my query so far:
SELECT c.campaign_id,
shop_id,
campaign_type,
contact_number AS users_mobile_numbers,
message FROM sms_campaign c
LEFT JOIN sms_recipients r
ON u.campaign_id = c.campaign_id
WHERE status = 0

Answer 1

In the LEFT JOIN, you will need to either move the filter status = 0 into a join condition, OR if you leave the filter in the WHERE clause, then status = 0 OR status IS NULL to avoid filtering out campaigns with no messages at all - I've done the first option.
As per the comment, you will need to GROUP the data by the campaign columns, and apply aggregate functions to all non-grouped columns, in order to guarantee just one row per group - GROUP_CONCAT will concatenate all text values in each GROUP. I've arbitrarily used MIN to resolve a value for shop and message, but you may need to adjust otherwise. (You can also do a DISTINCT in a GROUP CONCAT, if required).
SELECT
c.campaign_id,
MIN(shop_id) AS shop_id,
campaign_type,
GROUP_CONCAT(contact_number) AS users_mobile_numbers,
MIN(message) AS message
FROM sms_campaign c
LEFT JOIN sms_recipients r
ON u.campaign_id = c.campaign_id AND status = 0
GROUP BY c.campaign_id, campaign_type;

Answer 2

Move the condition on r.status to the ON clause of the outer join. (With the condition in the WHERE clause requiring r.status to be non-NULL, that will negate the outerness of the LEFT JOIN, making it equivalent to an INNER JOIN.)
Add a GROUP BY clause to collapse the rows.
Use a GROUP_CONCAT function to combine the values of contact_number. Column references which appear in the SELECT list but are not included in the GROUP BY clause should also be enclosed in aggregate expressions.)
SELECT c.campaign_id
, ...
, GROUP_CONCAT(DISTINCT r.contact_number ORDER BY r.contact_number) AS `c_numbers`
, MIN(r.message) AS `message`
FROM campaign c
LEFT
JOIN sms_recipients r
ON r.campaign_id = c.campaign_id
AND r.status = 0
GROUP BY c.campaign_id
The value returned by GROUP_CONCAT aggregate function is limited by max_group_concat_len variable. Longer values will be silently truncated to the maximum length.