CODEWITHSUNDEEP
mysqlsqljoingreatest-n-per-group
E.Ak
E.Ak

Reputation: 67

MySQL Inner Join Get Last Item of Joined Table

There are two tables:

Table name: ticket

+-------+---------+---------+-------------------+
|  id   |  title       |  closed    | param     |
+-------+--------------+------------+-----------+
| 1     | test1        | 0          | 1         |
| 2     | test2        | 1          | 1         |
| 3     | test3        | 0          | 1         |

Table name: ticket_event

+-------+---------+---------+-----------------+
|  id   |  ticket_id   |  event   | date      |
+-------+--------------+----------+-----------+
| 1     | 1            | OPENED   |           |
| 2     | 1            | CLOSED   |           |
| 3     | 2            | OPENED   |           |
+-------+--------------+----------+-----------+

I need to get the last record of ticket_event for each ticket. Result should be:

test1 CLOSED
test2 OPENED
test3 NULL

I tried this code but I get all records for ticket_event:

SELECT t1.title as t1Title, t2.event as t2Event FROM ticket t1 LEFT JOIN ticket_event t2 ON t1.id = t2.ticket_id

Upvotes: 0

Views: 83

Answers (2)

forpas
forpas

Reputation: 164069

You can join ticket to a query that returns the last event::

SELECT t.title, e.event
FROM ticket t LEFT JOIN (
  SELECT e.* from ticket_event e
  WHERE NOT EXISTS (
    SELECT 1 FROM ticket_event 
    WHERE ticket_id = e.ticket_id AND id > e.id
  )
) e 
ON t.id = e.ticket_id

See the demo.
Results:

| title | event  |
| ----- | ------ |
| test1 | CLOSED |
| test2 | OPENED |
| test3 |        |

Upvotes: 1

GMB
GMB

Reputation: 222432

A correlated subquery can do the trick:

select 
    t.title,
    (
        select te.event 
        from ticket_event te 
        where te.ticket_id = t.id 
        order by te.id desc 
        limit 1
    ) last_event
from ticket t

It is quite unclear which column in ticket_event you want to use for ordering. Using date would make sense, but that column is empty in your table, so I went for id. You can change that according to your real requirement.

Upvotes: 1

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