EXPLAIN PLAN FOR
In SQL Developer, you don't have to use EXPLAIN PLAN FOR statement. Press F10 or click the Explain Plan icon.
It will be then displayed in the Explain Plan window.
If you are using SQL*Plus then use DBMS_XPLAN.
For example,
SQL> EXPLAIN PLAN FOR
2 SELECT * FROM DUAL;
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------
Plan hash value: 272002086
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 2 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS FULL| DUAL | 1 | 2 | 2 (0)| 00:00:01 |
--------------------------------------------------------------------------
8 rows selected.
SQL>