How to delete an attachment from a ticket in OTRS (this example is from 
OTRS version 6; probably similar in older versions).

You will need to know the TicketID of the ticket you want to remove the 
attachment from. This example will use TicketID=533 because we dislike the 
attached cat picture ('kitty.jpg').

Search through the article_search_index table for the corresponding article_key:
MariaDB [otrs]> SELECT * FROM article_search_index WHERE ticket_id = 533 AND article_key = 'MIMEBase_AttachmentName';
+-------+-----------+------------+-------------------------+---------------+
| id    | ticket_id | article_id | article_key             | article_value |
+-------+-----------+------------+-------------------------+---------------+
| 31324 |       533 |       1500 | MIMEBase_AttachmentName | kitty.jpg     |
+-------+-----------+------------+-------------------------+---------------+

Find the corresponding attachment(s) in the article_data_mime_attachment table:
MariaDB [otrs]> SELECT id,article_id,filename,content_size,content_type FROM article_data_mime_attachment WHERE article_id = 1500;
+-----+------------+--------------+--------------+--------------------------------+
| id  | article_id | filename     | content_size | content_type                   |
+-----+------------+--------------+--------------+--------------------------------+
| 147 |       1500 | file-1       | 2211         | text/plain; charset="utf-8"    |
| 148 |       1500 | file-2       | 8234         | text/html; charset="utf-8"     |
| 149 |       1500 | kitty.jpg    | 51963        | image/jpg; name="kitty.jpg"    |
+-----+------------+--------------+--------------+--------------------------------+

Delete the attachment(s):
MariaDB [otrs]> DELETE FROM article_data_mime_attachment WHERE article_id = 1500 AND id = 149;
Query OK, 1 row affected (0.22 sec)

Job done!
Tags: OTRS, tickets, attachments, delete, remove, database