OracleµÄÓÅ»¯Æ÷ÓÐÁ½ÖÖÓÅ»¯·½Ê½(¶þ)
15. /*+USE_CONCAT*/
¶Ô²éѯÖеÄWHEREºóÃæµÄORÌõ¼þ½øÐÐת»»ÎªUNION ALLµÄ×éºÏ²éѯ. (ã¶®°¡,ÏÈ´æ×Å)
ÀýÈç:
select /*+use_concat */ * from emp where deptno=10 OR empno=7788;
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=2 Bytes=174)
1 0 TABLE ACCESS (FULL) OF 'EMP' (Cost=2 Card=2 Bytes=174)
16. /*+NO_EXPAND*/
¶ÔÓÚWHEREºóÃæµÄOR »òÕßIN-LISTµÄ²éѯÓï¾ä,
NO_EXPAND½«×èÖ¹Æä»ùÓÚÓÅ»¯Æ÷¶ÔÆä½øÐÐÀ©Õ¹.
SELECT /*+NO_EXPAND*/ * from EMP WHERE DEPTNO=10 AND job='MANAGER';
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1 Bytes=87)
1 0 TABLE ACCESS (FULL) OF 'EMP' (Cost=2 Card=1 Bytes=87)
17. /*+NOWRITE*/
½ûÖ¹¶Ô²éѯ¿éµÄ²éÑ¯ÖØÐ´²Ù×÷.
18. /*+REWRITE*/
¿ÉÒÔ½«ÊÓͼ×÷Ϊ²ÎÊý.
19. /*+MERGE(TABLE)*/
Äܹ»¶ÔÊÓͼµÄ¸÷¸ö²éѯ½øÐÐÏàÓ¦µÄºÏ²¢.
20. /*+NO_MERGE(TABLE)*/
¶ÔÓÚÓпɺϲ¢µÄÊÓͼ²»Ôٺϲ¢.
21. /*+ORDERED*/
¸ù¾Ý±í³öÏÖÔÚfromÖеÄ˳Ðò,ORDEREDʹORACLEÒÀ´Ë˳Ðò¶ÔÆäÁ¬½Ó.
SELECT /*+ORDERED*/ D.DNAME, E.ENAME,E.SAL from EMP E,DEPT D WHERE E.DEPTNO=D.DEPTNO;
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=5 Card=82 Bytes=4510)
1 0 HASH JOIN (Cost=5 Card=82 Bytes=4510)
2 1 TABLE ACCESS (FULL) OF 'EMP' (Cost=2 Card=82 Bytes=2706)
3 1 TABLE ACCESS (FULL) OF 'DEPT' (Cost=2 Card=82 Bytes=1804)
¶Ò»»ÏÂEMPºÍDEPTµÄ˳Ðò,µÃµ½
SELECT /*+ORDERED*/ D.DNAME, E.ENAME,E.SAL from DEPT D, EMP E WHERE E.DEPTNO=D.DEPTNO;
Execution Plan
--------------------
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