The index unique scan is good for getting one row from and index and returning the rowid. You will get a index unique scan if you have a unique index or primary key on a table.
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| In this example; we created an unique index on object_id. When we executed the query, the optimizer did a index unique scan. |
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| And the index unique scan did just what it was designed to do, select one row. |
| Now lets try this with a normal btree index.
SQL> drop index t1_idx; Index dropped. SQL> create index t1_idx on t1(object_id); Index created. SQL> analyze index t1_idx compute statistics; Index analyzed. |
As you can see here, because we uses a normal index th e The optimizer decided to do a index range scan. |
Next we will be covering Index range scan.