How to condense a column like this? - mysql

Question

I've tried finding something like this, but to no avail...
This is about a system of tables for a customer management system. In particular, I need to create a note history for each customer.
So, I have a table 'customers' with the columns customers.customer_ID, customers.lastname, customers.firstname, customers.postal_code, customers.city and customers.street;
and another table 'notes' with the columns notes.note_ID, notes.customer_ID, notes.subject, notes.description and notes.entered_on
Now I need to create a third table search which condenses much of the information above. It has the tables search.contact_ID, search.name, search.address and search.history. This is supposed to look like this:
contacts:
contact_ID | lastname | firstname | ...
------------+-----------+-----------+-----
1 | Doe | John | ...
2 | Dane | Jane | ...
note:
note_ID | contact_ID | subject | description | entered_on
--------+---------------+-----------------------+-----------------------+----------------
1 | 1 | call received | John Doe called us to | 2014-05-03
| | | ask for an offer |
2 | 1 | offer made | We called John Doe to | 2014-06-03
| | | submit our offer |
3 | 2 | advertisement call | We called Jane Dane to| 2014-06-03
| | | inform her of our |
| | | latest offer |
4 | 1 | offer accepted | John Doe called to | 2014-08-03
| | | accept our offer |
search:
contact_ID | name | address | history
------------+---------------+---------------------------------+-------------------
1 | Doe, John | 55 Main Street, 12345 Oldtown | 'On 2014-08-03 offer accepted: John Doe accepted our offer.
| | | On 2014-06-03 offer made: We called John Doe to submit our offer.
| | | On 2014-05-03 call received: John Doe called us to ask for an offer.'
2 | Dane, Jane | 111 Wall Street, 67890 Newtown | 'On 2014-06-03 advertisement call: We called Jane Dane to submit our offer.'
While I can deal with much of the rest, I have no idea how to generate the history information. My idea was as follows
WHILE
customers.customer_ID = note.customer_ID
AND
note.entered_on = GREATEST(note.entered_on)
DO
SET customers.note_history = CONCAT_WS(' | ', CONCAT_WS(': ',note.subject,note.description), customers.note_history);
But that one isn't necessarily chronological. Also how do I transform that into a statement compatible with the SELECT INTO used for the creation of the rest of the table?

Answer 1

Sounds like a case for a Group-By, along with GROUP_CONCAT
CREATE TABLE search (PRIMARY KEY(contact_ID))
SELECT contact_ID, CONCAT(lastname,', ',firstname) AS name, address,
GROUP_CONCAT(CONCAT('On ',entered_on,' ',subject,': ',description)
ORDER BY note_ID SEPARATOR "\n") AS history
FROM contacts LEFT JOIN note USING (contact_ID)
GROUP BY contact_ID
If dont want to use CREATE TABLE .. SELECT ... , can first just create (or truncate!) the table, and then use INSERT INTO ... SELECT ... instead.