函数索引（Function-based indexes）只有在where条件使用了与索引中相同的基于相同列的函数时才起作用。 duzz$scott@orcl>set autotrace on duzz$scott@orcl>create table t1 as select * from dept; Table created. Elapsed: 00:00:00.01 duzz$scott@orcl>create index loc_idx on t1(upper(loc)); Index created. Elapsed: 00:00:00.06 duzz$scott@orcl>select * from t1 where deptno=20; DEPTNO DNAME LOC ---------- ------------------------------------------ ------------ 20 RESEARCH DALLAS Elapsed: 00:00:00.00 Execution Plan ---------------------------------------------------------- Plan hash value: 3617692013 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 30 | 3 (0)| 00:00:01 | |* 1 | TABLE ACCESS FULL| T1 | 1 | 30 | 3 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("DEPTNO"=20) Note ----- - dynamic sampling used for this statement Statistics ---------------------------------------------------------- 48 recursive calls 0 db block gets 12 consistent gets 0 physical reads 0 redo size 533 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed duzz$scott@orcl>select * from t1 where loc='DALLAS'; DEPTNO DNAME LOC ---------- ------------------------------------------ ----------------- 20 RESEARCH DALLAS Elapsed: 00:00:00.00 Execution Plan ---------------------------------------------------------- Plan hash value: 3617692013 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 30 | 3 (0)| 00:00:01 | |* 1 | TABLE ACCESS FULL| T1 | 1 | 30 | 3 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("LOC"='DALLAS') Note ----- - dynamic sampling used for this statement Statistics ---------------------------------------------------------- 5 recursive calls 0 db block gets 8 consistent gets 0 physical reads 0 redo size 533 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed duzz$scott@orcl>select * from t1 where upper(loc)='DALLAS'; DEPTNO DNAME LOC ---------- ------------------------------------------ ---------------------- 20 RESEARCH DALLAS Elapsed: 00:00:00.01 Execution Plan ---------------------------------------------------------- Plan hash value: 3763008475 --------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 30 | 2 (0)| 00:00:01 | | 1 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 30 | 2 (0)| 00:00:01 | |* 2 | INDEX RANGE SCAN | LOC_IDX | 1 | | 1 (0)| 00:00:01 | --------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access(UPPER("LOC")='DALLAS') Note ----- - dynamic sampling used for this statement Statistics ---------------------------------------------------------- 28 recursive calls 0 db block gets 9 consistent gets 0 physical reads 0 redo size 533 bytes sent via SQL*Net to client 385 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed duzz$scott@orcl>

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