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ORACLE SQLÐÔÄÜÓÅ»¯ÏµÁÐ
1. ·ÃÎÊTableµÄ·½Ê½
ORACLE ²ÉÓÃÁ½ÖÖ·ÃÎʱíÖмǼµÄ·½Ê½:
a. È«±íɨÃè
È«±íɨÃè¾ÍÊÇ˳ÐòµØ·ÃÎʱíÖÐÿÌõ¼Ç¼. ORACLE²ÉÓÃÒ»´Î¶ÁÈë¶à¸öÊý¾Ý¿é(database block)µÄ·½Ê½ÓÅ»¯È«±íɨÃè.
b. ͨ¹ýROWID·ÃÎʱí
Äã¿ÉÒÔ²ÉÓûùÓÚROWIDµÄ·ÃÎÊ·½Ê½Çé¿ö,Ìá¸ß·ÃÎʱíµÄЧÂÊ, , ROWID°üº¬Á˱íÖмǼµÄÎïÀíλÖÃÐÅÏ¢..ORACLE²ÉÓÃË÷Òý(INDEX)ʵÏÖÁËÊý¾ÝºÍ´æ·ÅÊý¾ÝµÄÎïÀíλÖÃ(ROWID)Ö®¼äµÄÁªÏµ. ͨ³£Ë÷ÒýÌṩÁË¿ìËÙ·ÃÎÊROWIDµÄ·½·¨,Òò´ËÄÇЩ»ùÓÚË÷ÒýÁеIJéѯ¾Í¿ÉÒԵõ½ÐÔÄÜÉϵÄÌá¸ß.
2. ¹²ÏíSQLÓï¾ä
ΪÁ˲»Öظ´½âÎöÏàͬµÄSQLÓï¾ä,ÔÚµÚÒ»´Î½âÎöÖ®ºó, ORACLE½«SQLÓï¾ä´æ·ÅÔÚÄÚ´æÖÐ.Õâ¿éλÓÚϵͳȫ¾ÖÇøÓòSGA(system global area)µÄ¹²Ïí³Ø(shared buffer pool)ÖеÄÄÚ´æ¿ÉÒÔ±»ËùÓеÄÊý¾Ý¿âÓû§¹²Ïí. Òò´Ë,µ±ÄãÖ´ÐÐÒ»¸öSQLÓï¾ä(ÓÐʱ±»³ÆÎªÒ»¸öÓαê)ʱ,Èç¹ûËüºÍ֮ǰµÄÖ´ÐйýµÄÓï¾äÍêÈ«Ïàͬ, ORACLE¾ÍÄܺܿì»ñµÃÒѾ±»½âÎöµÄÓï¾äÒÔ¼°×îºÃµÄÖ´Ðз¾¶. ORACLEµÄÕâ¸ö¹¦ÄÜ´ó´óµØÌá¸ßÁËSQLµÄÖ´ÐÐÐÔÄܲ¢½ÚÊ¡ÁËÄÚ´æµÄʹÓÃ.
¿ÉϧµÄÊÇORACLEÖ»¶Ô¼òµ¥µÄ±íÌṩ¸ßËÙ»º³å(cache buffering) ,Õâ¸ö¹¦Äܲ¢²»ÊÊÓÃÓÚ¶à±íÁ¬½Ó²éѯ.
Êý¾Ý¿â¹ÜÀíÔ±±ØÐëÔÚinit.oraÖÐΪÕâ¸öÇøÓòÉèÖúÏÊʵIJÎÊý,µ±Õâ¸öÄÚ´æÇøÓòÔ½´ó,¾Í¿ÉÒÔ±£Áô¸ü¶àµÄÓï¾ä,µ±È»±»¹²ÏíµÄ¿ÉÄÜÐÔÒ²¾ÍÔ½´óÁË.
µ±ÄãÏòORACLE Ìá½»Ò»¸öSQLÓï¾ä,ORACLE»áÊ×ÏÈÔÚÕâ¿éÄÚ´æÖвéÕÒÏàͬµÄÓï¾ä.
ÕâÀïÐèҪעÃ÷µÄÊÇ,ORACLE¶ÔÁ½Õß²ÉÈ¡µÄÊÇÒ»ÖÖÑϸñÆ¥Åä,Òª´ï³É¹²Ïí,SQLÓï¾ä±ØÐëÍêÈ«Ïàͬ(°üÀ¨¿Õ¸ñ,»»ÐеÈ).
¹²ÏíµÄÓï¾ä±ØÐëÂú×ãÈý¸öÌõ¼þ:
A. ×Ö·û¼¶µÄ±È½Ï:
µ±Ç°±»Ö´ÐеÄÓï¾äºÍ¹²Ïí³ØÖеÄÓï¾ä±ØÐëÍêÈ«Ïàͬ.
ÀýÈç:
SELECT * from EMP;
ºÍÏÂÁÐÿһ¸ö¶¼²»Í¬
SELECT * from EMP;
Select * from Emp;
SELECT * from EMP;
B. Á½¸öÓï¾äËùÖ¸µÄ¶ÔÏó±ØÐëÍêÈ«Ïàͬ:
ÀýÈç:
Óû§ ¶ÔÏóÃû ÈçºÎ·ÃÎÊ
Jack sal_limit private synonym
Work_city public synonym
Plant_detail public synonym
Jill sal_limit private synonym
Work_city public synonym
Plant_detail table owner
¿¼ÂÇÒ»ÏÂÏÂÁÐSQLÓï¾äÄÜ·ñÔÚÕâÁ½¸öÓû§Ö®¼ä¹²Ïí.
SQL
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select max(sal_cap) from sal_limit;
²»ÄÜ
ÿ¸öÓû§¶¼ÓÐÒ»¸öprivate synonym - sal_limit , ËüÃÇÊDz»Í¬µÄ¶ÔÏó
select count(*0 from work_city where sdesc like 'NEW%';
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