To reclaim the free space

Method 1.
To reclaim the free space you can Move the table to the tablespace that it currently belongs, ie. Doing nothing but just moving it to itself.

This can be only done if it is an LMT (locally managed tablespace), we tend to move the data to the "front" of the file (allowing you to shrink the file)
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If you are not using LMTs then try 'alter tablespace tblspc-name coalesce'


Method 2

1) delete million rows from table A

2) create table B as select * from table A

3) truncate table A

4) insert into table A select * from table B

5) drop table B

6) rebuild indexes


1) alter table (tablename) move;
2) rebuild all the UNUSABLE indexes on the table.