（「某某」！=「某某」），而不是（「某某」 =「某某」）之間有什麼區別

Question

有沒有。雖然我問Oracle數據庫中的情況下('xyz' != 'xyz')和NOT ('xyz' = 'xyz')

之間的任何差別，但也想知道其他語言的相同情況。

差異主要是像處理速度和所有背景的東西。

Answer 1

您是否看到有什麼不同？

測試用例：

SQL> SELECT * FROM dual 
    2 WHERE ('xyz' != 'xyz'); 

no rows selected 

SQL> 
SQL> SELECT * FROM dual 
    2 WHERE NOT ('xyz' = 'xyz'); 

no rows selected 

在上述查詢兩者應用的濾波器是相同濾波器（NULL IS NOT NULL）。

執行計劃：

SQL> EXPLAIN PLAN FOR 
    2 SELECT * FROM dual 
    3 WHERE ('xyz' != 'xyz'); 

Explained. 

SQL> 
SQL> SELECT * FROM TABLE(dbms_xplan.display); 

PLAN_TABLE_OUTPUT 
-------------------------------------------------------------------------------- 
Plan hash value: 3752461848 

--------------------------------------------------------------------------- 
| Id | Operation   | Name | Rows | Bytes | Cost (%CPU)| Time  | 
--------------------------------------------------------------------------- 
| 0 | SELECT STATEMENT |  |  1 |  2 |  0 (0)|   | 
|* 1 | FILTER   |  |  |  |   |   | 
| 2 | TABLE ACCESS FULL| DUAL |  1 |  2 |  2 (0)| 00:00:01 | 
--------------------------------------------------------------------------- 

Predicate Information (identified by operation id): 

PLAN_TABLE_OUTPUT 
-------------------------------------------------------------------------------- 
--------------------------------------------------- 

    1 - filter(NULL IS NOT NULL) 

14 rows selected. 

SQL> 
SQL> EXPLAIN PLAN FOR 
    2 SELECT * FROM dual 
    3 WHERE NOT ('xyz' = 'xyz'); 

Explained. 

SQL> 
SQL> SELECT * FROM TABLE(dbms_xplan.display); 

PLAN_TABLE_OUTPUT 
-------------------------------------------------------------------------------- 
Plan hash value: 3752461848 

--------------------------------------------------------------------------- 
| Id | Operation   | Name | Rows | Bytes | Cost (%CPU)| Time  | 
--------------------------------------------------------------------------- 
| 0 | SELECT STATEMENT |  |  1 |  2 |  0 (0)|   | 
|* 1 | FILTER   |  |  |  |   |   | 
| 2 | TABLE ACCESS FULL| DUAL |  1 |  2 |  2 (0)| 00:00:01 | 
--------------------------------------------------------------------------- 

Predicate Information (identified by operation id): 

PLAN_TABLE_OUTPUT 
-------------------------------------------------------------------------------- 
--------------------------------------------------- 

    1 - filter(NULL IS NOT NULL) 

14 rows selected. 

SQL> 

沒有區別。