|
--1:无ORDER BY排序的写法。(效率最高)
--(经过测试,此方法成本最低,只嵌套一层,速度最快!即使查询的数据量再大,也几乎不受影响,速度依然!)
SELECT *
FROM (SELECT ROWNUM AS rowno, t.*
FROM emp t
WHERE hire_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060731', 'yyyymmdd')
AND ROWNUM = 10;
--2:有ORDER BY排序的写法。(效率最高)
--(经过测试,此方法随着查询范围的扩大,速度也会越来越慢哦!)
SELECT *
FROM (SELECT tt.*, ROWNUM AS rowno
FROM ( SELECT t.*
FROM emp t
WHERE hire_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060731', 'yyyymmdd')
ORDER BY create_time DESC, emp_no) tt
WHERE ROWNUM = 10;
=================================================================================
=======================垃圾但又似乎很常用的分页写法==========================
=================================================================================
--3:无ORDER BY排序的写法。(建议使用方法1代替)
--(此方法随着查询数据量的扩张,速度会越来越慢哦!)
SELECT *
FROM (SELECT ROWNUM AS rowno, t.*
FROM k_task t
WHERE flight_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060731', 'yyyymmdd')) table_alias
WHERE table_alias.rowno = 10;
--TABLE_ALIAS.ROWNO between 10 and 100;
--4:有ORDER BY排序的写法.(建议使用方法2代替)
--(此方法随着查询范围的扩大,速度会越来越慢哦!)
SELECT *
FROM (SELECT tt.*, ROWNUM AS rowno
FROM ( SELECT *
FROM k_task t
WHERE flight_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060531', 'yyyymmdd')
ORDER BY fact_up_time, flight_no) tt) table_alias
WHERE table_alias.rowno BETWEEN 10 AND 20;
--5另类语法。(有ORDER BY写法)
--(语法风格与传统的SQL语法不同,不方便阅读与理解,为规范与统一标准,不推荐使用。)
WITH partdata AS
(
SELECT ROWNUM AS rowno, tt.*
FROM ( SELECT *
FROM k_task t
WHERE flight_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060531', 'yyyymmdd')
ORDER BY fact_up_time, flight_no) tt
WHERE ROWNUM = 10;
--6另类语法 。(无ORDER BY写法)
WITH partdata AS
(
SELECT ROWNUM AS rowno, t.*
FROM k_task t
WHERE flight_date BETWEEN TO_DATE ('20060501', 'yyyymmdd')
AND TO_DATE ('20060531', 'yyyymmdd')
AND ROWNUM = 10;
yangtingkun分析:
--- from :http://yangtingkun.itpub.net/post/468/100278
Oracle的分页查询语句基本上可以按照本文给出的格式来进行套用。
分页查询格式:
SELECT *
FROM (SELECT a.*, ROWNUM rn
FROM (SELECT *
FROM table_name) a
WHERE ROWNUM = 21
其中最内层的查询SELECT * FROM TABLE_NAME表示不进行翻页的原始查询语句。ROWNUM = 21控制分页查询的每页的范围。
上面给出的这个分页查询语句,在大多数情况拥有较高的效率。分页的目的就是控制输出结果集大小,将结果尽快的返回。在上面的分页查询语句中,这种考虑主要体现在WHERE ROWNUM |
|
|