Index size

I think this feature came around ages ago (10.2?) but I’m still always impressed by it every time I use it.

You can run EXPLAIN on a CREATE INDEX command

SQL> explain plan for create index IX on MY_TABLE ( bet_account_num );

Explained.

--------------------------------------------------------------------------------------
| Id  | Operation              | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | CREATE INDEX STATEMENT |             |   213K|   626K|   833   (1)| 00:00:11 |
|   1 |  INDEX BUILD NON UNIQUE| IX          |       |       |            |          |
|   2 |   SORT CREATE INDEX    |             |   213K|   626K|            |          |
|   3 |    TABLE ACCESS FULL   | MY_TABLE    |   213K|   626K|   712   (2)| 00:00:09 |
--------------------------------------------------------------------------------------

Note
-----
- estimated index size: 5128K bytes

and you get a nice little estimate of how big your index will be…..Awesome!