常用的Oracle查询语句
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!
sql语句如下:
SELECT *
FROM (Select ROWNUM AS ROWNO, T.*
from k_task T
where Flight_date between to_date('20060501', 'yyyymmdd') and
to_date('20060731', 'yyyymmdd')
AND ROWNUM <= 20) TABLE_ALIAS
WHERE TABLE_ALIAS.ROWNO >= 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!
SELECT *
FROM (SELECT TT.*, ROWNUM AS ROWNO
FROM (Select t.*
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 <= 20) TABLE_ALIAS
where TABLE_ALIAS.rowno >= 10;
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!
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 <= 20
AND 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,速度也会越来越慢!
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)
该语法风格与传统的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。此处贴出代码供大家参考之用。
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 <= 20)
Select * from partdata where rowno >= 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 <= 20)
Select * from partdata where Rowno >= 10;