G-9603
Warning
Never reference an unknown table/alias.
Reason
There are various hints that reference a table or view. If the table or view reference in the hint is neither a table name nor an alias, then the hint is ignored by the Oracle Database.
Example
Non-Compliant Example
select --+ leading(emps depts)
*
from emp
join dept on emp.deptno = dept.deptno;
select * from dbms_xplan.display_cursor(format => 'basic +hint_report');
/*
------------------------------------------------
| Id | Operation | Name |
------------------------------------------------
| 0 | SELECT STATEMENT | |
| 1 | MERGE JOIN | |
| 2 | TABLE ACCESS BY INDEX ROWID| DEPT |
| 3 | INDEX FULL SCAN | PK_DEPT |
| 4 | SORT JOIN | |
| 5 | TABLE ACCESS FULL | EMP |
------------------------------------------------
Hint Report (identified by operation id / Query Block Name / Object Alias):
Total hints for statement: 1 (U - Unused (1))
---------------------------------------------------------------------------
1 - SEL$58A6D7F6
U - leading(emps depts)
*/Issues
| Line | Column | Message |
|---|---|---|
| 1 | 20 | Unknown table/alias emps in leading hint. |
| 1 | 25 | Unknown table/alias depts in leading hint. |
Compliant Solution - ★★★★★
select --+ leading(emp dept)
*
from emp
join dept on emp.deptno = dept.deptno;
select * from dbms_xplan.display_cursor(format => 'basic +hint_report');
/*
-----------------------------------
| Id | Operation | Name |
-----------------------------------
| 0 | SELECT STATEMENT | |
| 1 | HASH JOIN | |
| 2 | TABLE ACCESS FULL| EMP |
| 3 | TABLE ACCESS FULL| DEPT |
-----------------------------------
Hint Report (identified by operation id / Query Block Name / Object Alias):
Total hints for statement: 1
---------------------------------------------------------------------------
1 - SEL$58A6D7F6
- leading(emp dept)
*/