Index uniqueness Scan (index unique scan)

The index unique scan, which is a scan of a unique index, applies only to the target SQL that is the equivalent query in the WHERE condition. Because the scanned object is a unique index, the results of the index uniqueness scan will return at most one record.

Empno is primary key in the EMP table, corresponding to a unique index

[Email protected]> SELECT * from emp where empno=7369;

Execution plan
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Plan Hash value:2949544139

--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU) | Time |
--------------------------------------------------------------------------------------
| 0 |        SELECT STATEMENT |     |    1 |     38 | 1 (0) | 00:00:01 |
|  1 | TABLE ACCESS by INDEX rowid|     EMP |    1 |     38 | 1 (0) | 00:00:01 |
|* 2 | INDEX UNIQUE SCAN |     Pk_emp |       1 |     | 0 (0) | 00:00:01 |
--------------------------------------------------------------------------------------

predicate information (identified by Operation ID):
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2-access ("EMPNO" =7369)

Statistical information
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Recursive calls
0 db Block gets
Consistent gets
Physical Reads
0 Redo Size
898 bytes sent via sql*net to client
533 Bytes received via sql*net from client
1 sql*net roundtrips To/from Client
8 Sorts (memory)
0 Sorts (disk)
1 rows processed

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View Code

As you can see from the above, the execution plan for "select * from emp where empno=7369" is an index-unique scan.

Index uniqueness Scan (index unique scan)