We have a multi-GB InnoDB MariaDB (recently switched from MySQL). For some reason, the value of innodb_file_per_table changed to ON (we wanted only one innodb data file explicitely). So when I ran an ALTER TABLE statement on one of the big tables, it created a separate .ibd file which now occupies 35GB even though I had takes measures to make ~100GB space free in the shared tablespace (ibdata1).
How can I re-integrate the data from this file back into the shared tablespace? I thought maybe DISCARD TABLESPACE would do that, but this just deletes the file and the data in it (I tested it with a sample table of course).