Oracle can materialize the intermediate results of a table join in the temporary segment set for your session.
Since it's a one-off table that is deleted after the query is complete, its statistics are not stored.
However, you can estimate its size by building a plan for the query and looking at ROWS
parameters of the appropriate operation:
EXPLAIN PLAN FOR
WITH q AS
(
SELECT /*+ MATERIALIZE */
e1.value AS val1, e2.value AS val2
FROM t_even e1, t_even e2
)
SELECT COUNT(*)
FROM q
SELECT *
FROM TABLE(DBMS_XPLAN.display())
Plan hash value: 3705384459
---------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 43G (5)|999:59:59 |
| 1 | TEMP TABLE TRANSFORMATION | | | | | |
| 2 | LOAD AS SELECT | | | | | |
| 3 | MERGE JOIN CARTESIAN | | 100T| 909T| 42G (3)|999:59:59 |
| 4 | TABLE ACCESS FULL | T_ODD | 10M| 47M| 4206 (3)| 00:00:51 |
| 5 | BUFFER SORT | | 10M| 47M| 42G (3)|999:59:59 |
| 6 | TABLE ACCESS FULL | T_ODD | 10M| 47M| 4204 (3)| 00:00:51 |
| 7 | SORT AGGREGATE | | 1 | | | |
| 8 | VIEW | | 100T| | 1729M (62)|999:59:59 |
| 9 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6604_2660595 | 100T| 909T| 1729M (62)|999:59:59 |
---------------------------------------------------------------------------------------------------------
Here, the materialized table is called SYS_TEMP_0FD9D6604_2660595
and the estimated record count is 100T
(100,000,000,000,000
records)