rob@XE:11g2> set autotrace traceonly explain
rob@XE:11g2> SELECT COUNT(*) FROM
2 (SELECT given_name FROM top_french_names
3 UNION
4 SELECT given_name FROM top_usa_names
5 );
Elapsed: 00:00:00.08
Execution Plan
==========================================================
Plan hash value: 1581671293
------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|Time |
------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 8 (25)|00:00:01 |
| 1 | SORT AGGREGATE | | 1 | | | |
| 2 | VIEW | | 400 | | 8 (25)|00:00:01 |
| 3 | SORT UNIQUE | | 400 | 2800 | 8 (63)|00:00:01 |
| 4 | UNION-ALL | | | | | |
| 5 | TABLE ACCESS FULL| TOP_FRENCH_NAMES | 200 | 1400 | 3 (0)|00:00:01 |
| 6 | TABLE ACCESS FULL| TOP_USA_NAMES | 200 | 1400 | 3 (0)|00:00:01 |
------------------------------------------------------------------------------------------
rob@XE:11g2> SELECT COUNT(*) FROM
2 (SELECT given_name FROM top_french_names
3 UNION ALL
4 SELECT given_name FROM top_usa_names
5 );
Elapsed: 00:00:00.04
Execution Plan
==========================================================
Plan hash value: 2045709238
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time|
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 6 (0)| 00:00:01|
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | VIEW | | 400 | 6 (0)| 00:00:01|
| 3 | UNION-ALL | | | | |
| 4 | TABLE ACCESS FULL| TOP_FRENCH_NAMES | 200 | 3 (0)| 00:00:01|
| 5 | TABLE ACCESS FULL| TOP_USA_NAMES | 200 | 3 (0)| 00:00:01|
---------------------------------------------------------------------------------