Populate one table with selected data from two others tables - mysql

Question

I have a table that I am trying to populate with our open tickets and the last followup they received, columns below, this is called "glpi_plugin_ns_followup":
ticket_number[int(11)], datetime_created[datetime], requester[int(11)], title[longtext], description[longtext], followup_datetime[datetime], last_followup[longtext], technician_user[int(11)]
The tables I am pulling from are glpi_tickets and glpi_ticketfollowups
glpi_tickets
id[int(11)], entities_id[int(11)], name[varchar(255)], date[datetime], closedate[datetime], solvedate[datetime], date_mod[datetime], users_id_lastupdater[int(11)], status[int(11)], users_id_recipient[int(11)], requesttypes_id[int(11)], content, urgency[int(11)], impact[int(11)], priority[int(11)], itilcategories_id[int(11)], type[int(11)], solutiontypes_id[int(11)], solution, global_validation[int(11)], slas_id[int(11)], slalevels_id[int(11)], due_date[datetime], begin_waiting_date[datetime], sla_waiting_duration[int(11)], waiting_duration[int(11)], close_delay_stat[int(11)], solve_delay_stat[int(11)], takeintoaccount_delay_stat[int(11)], actiontime[int(11)], is_deleted[tinyint(1)], locations_id[int(11)], validation_percent[int(11)]
glpi_ticketfollowups
id[int(11)], tickets_id[int(11)], date[datetime], users_id[int(11)], content[longtext], is_private[tinyint(11)], requesttypes_id[int(11)]
The common identifier across all three are as follows:
glpi_tickets = id
glpi_ticketfollowups = tickets_id
glpi_plugin_ns_followup = ticket_number
I've managed to insert the first five columns by using the below query:
TRUNCATE glpi_plugin_ns_followup;
INSERT INTO glpi_plugin_ns_followup (ticket_number, datetime_created, requester, title, description)
SELECT Id, date, users_id_recipient, name, content FROM glpi.glpi_tickets
WHERE is_deleted = 0 and status !=6 and status !=5;
However I am struggling to fill in the last 3 columns with the relevant updates, so far I have tried using this code but it doesn't work:
UPDATE glpi_plugin_ns_followup
SET followup_datetime = (SELECT date from glpi_ticketfollowups where glpi_ticketfollowups.tickets_id = glpi_plugin_ns_followup.ticket_number),
last_followup = (SELECT content from glpi_ticketfollowups where glpi_ticketfollowups.tickets_id = glpi_plugin_ns_followup.ticket_number),
technician_user = (SELECT users_id from glpi_ticketfollowups where glpi_ticketfollowups.tickets_id = glpi_plugin_ns_followup.ticket_number)
This gives me the response:
Error Code: 1242. Subquery returns more than 1 row
Which it should as I'm trying to update multiple rows, or the error may be because there are multiple followups per ticket. I have a feeling I may be going at this from entirely the wrong angle. If someone can assist me and put me back on the right track that would be much appreciated.
I can supply sample data if needed but it will take a while to gather and censor it ;-)
EDIT: As per Kamil's suggestions with max() I have managed to get the date fields to work:
UPDATE glpi_plugin_ns_followup
SET followup_datetime = (SELECT max(date) from glpi_ticketfollowups where glpi_ticketfollowups.tickets_id = glpi_plugin_ns_followup.ticket_number GROUP BY tickets_id)
However I cannot get it to work for content or technician_user, if I can pull the newest date/times for the last time a followup was added to a ticket can I modify anything to pull in the content and technician_user as well?
EDIT2: tried adding GROUP BY t.id; at the end of your initial solution but it does not use the newest followup for the tickets.
EDIT3:Have tried the following, it pulls in the correct date/time but the wrong content
TRUNCATE glpi_plugin_ns_followup;
INSERT INTO glpi_plugin_ns_followup (ticket_number, datetime_created, requester, title, description, followup_datetime, last_followup, technician_user)
SELECT
t.id, t.date, t.users_id_recipient, t.name, t.content,
tf.datetime, tf.content, tf.users_id
FROM
glpi.glpi_tickets t
LEFT JOIN (SELECT max(date) as datetime, content, users_id, tickets_id
FROM glpi_ticketfollowups
GROUP BY tickets_id) tf ON
t.id = tf.tickets_id
WHERE
t.is_deleted = 0
and t.status NOT IN (5,6)
GROUP BY t.id;
Thanks
iFr4g

Answer 1

You could combine both of those statements into one and only issue INSERT command. However, this will multiply your rows from glpi_tickets if more than one matching row exists in glpi_ticketfollowups fetched with the condition t.id = tf.tickets_id.
I've added a LEFT JOIN and slightly changed the WHERE clause to save some coding.
INSERT INTO glpi_plugin_ns_followup (ticket_number, datetime_created, requester, title, description, followup_datetime, last_followup, technician_user)
SELECT
t.id, t.date, t.users_id_recipient, t.name, t.content,
tf.date, tf.content, tf.users_id
FROM
glpi.glpi_tickets t
LEFT JOIN glpi_ticketfollowups tf ON
t.id = tf.tickets_id
WHERE
t.is_deleted = 0
and t.status NOT IN (5,6)
If you need only one row per glpi_tickets table in your destination table, then what you are looking for is a way to get only one row from glpi_ticketfollowups per a ticket. This could be achieved by adding a GROUP BY clause and choosing appropriate logic of getting one value, for example: max() or min(). Remember, that issuing an aggregate function over 3 values will not bring you result from one row, but an aggregate result from entire dataset. This could be avoided by doing it the way you started - insert and update by adding a LIMIT clause.
Edit after comments:
Since you need last followup for a every ticket and you are sure that are dates per ticket are unique you could do a self-join calculating maximum date per ticket in glpi_ticketfollowups and then LEFT JOIN that to your glpi_tickets table:
INSERT INTO glpi_plugin_ns_followup (ticket_number, datetime_created, requester, title, description, followup_datetime, last_followup, technician_user)
SELECT
t.id, t.date, t.users_id_recipient, t.name, t.content,
tf.date, tf.content, tf.users_id
FROM
glpi.glpi_tickets t
LEFT JOIN (
SELECT allf.tickets_id, allf.date, allf.content, allf.users_id
FROM glpi_ticketfollowups allf
INNER JOIN (
SELECT tickets_id, MAX(date) AS date
FROM glpi_ticketfollowups
GROUP BY tickets_id
) lastf ON
allf.tickets_id = lastf.tickets_id
AND allf.date = lastf.date
) tf ON
t.id = tf.tickets_id
WHERE
t.is_deleted = 0
and t.status NOT IN (5,6)