How to check what indexes are used in query for Oracle

Here I'm going to describe how to get execution plan result for specific query. For example we have a table with test data:

CREATE TABLE indexed_data (
  id NUMBER(19,0) NOT NULL CONSTRAINT indexed_data_pk PRIMARY KEY,
  data NUMBER(19,0) NOT NULL
);
CREATE INDEX indexed_data_data_inx ON indexed_data (
  data
) NOLOGGING;

insert into indexed_data(id, data) values (1, 1);
insert into indexed_data(id, data) values (2, 2);
insert into indexed_data(id, data) values (3, 3);

And want to know is indexed_data_data_inx index used in query:

SELECT * from indexed_data WHERE data = 0;

This two queries will helps you:

EXPLAIN PLAN
SET statement_id = 'indexed_data_ex_plan' FOR
SELECT * from indexed_data WHERE data = 0;
SELECT PLAN_TABLE_OUTPUT FROM TABLE(DBMS_XPLAN.DISPLAY(NULL, 'indexed_data_ex_plan','BASIC'));

As result you will get:

Plan hash value: 1246571312

-------------------------------------------------------------
| Id  | Operation                                                | Name                                           |
-------------------------------------------------------------
|   0 | SELECT STATEMENT                          |                                                      |
|   1 |  TABLE ACCESS BY INDEX ROWID | INDEXED_DATA                      |
|   2 |   INDEX RANGE SCAN                        | INDEXED_DATA_DATA_INX |
-------------------------------------------------------------