索引唯一性掃描（INDEX UNIQUE SCAN）是針對唯一性索引（UNIQUE INDEX）的掃描，它僅僅適用於where條件裡是等值查詢的目標SQL。因為掃描的物件是唯一性索引，所以索引唯一性掃描的結果至多隻會返回一條記錄。
Emp表中empno為primary key，對應一個unique index
SCOTT@PDBORCL> select * from emp where empno=7369;
執行計劃
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Plan hash value: 2949544139
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| 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)
統計資訊
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69 recursive calls
0 db block gets
95 consistent gets
21 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
SCOTT@PDBORCL>
從上述顯示內容可以看出，"select * from emp where empno=7369"的執行計劃走的是索引唯一性掃描