使用Oracle特有的查詢文法, 可以達到事半功倍的效果
1. 樹查詢
create table tree (
id number(10) not null primary key,
name varchar2(100) not null,
super number(10) not null // 0 is root
);
-- 從子到父
select * from tree start with id = ? connect by id = prior super
-- 從父到子
select * from tree start with id = ? connect by prior id = super
-- 整棵樹
select * from tree start with super = 0 connect by prior id = super
2. 分頁查詢
select * from (
select my_table.*, rownum my_rownum from (
select name, birthday from employee order by birthday
) my_table where rownum < 120
) where my_rownum >= 100;
3. 累加查詢, 以scott.emp為例
select empno, ename, sal, sum(sal) over(order by empno) result from emp;
EMPNO ENAME SAL RESULT
---------- ---------- ---------- ----------
7369 SMITH 800 800
7499 ALLEN 1600 2400
7521 WARD 1250 3650
7566 JONES 2975 6625
7654 MARTIN 1250 7875
7698 BLAKE 2850 10725
7782 CLARK 2450 13175
7788 SCOTT 3000 16175
7839 KING 5000 21175
7844 TURNER 1500 22675
7876 ADAMS 1100 23775
7900 JAMES 950 24725
7902 FORD 3000 27725
7934 MILLER 1300 29025
4. 進階group by
select decode(grouping(deptno),1,'all deptno',deptno) deptno,
decode(grouping(job),1,'all job',job) job,
sum(sal) sal
from emp
group by ROLLUP(deptno,job);
DEPTNO JOB SAL
---------------------------------------- --------- ----------
10 CLERK 1300
10 MANAGER 2450
10 PRESIDENT 5000
10 all job 8750
20 CLERK 1900
20 ANALYST 6000
20 MANAGER 2975
20 all job 10875
30 CLERK 950
30 MANAGER 2850
30 SALESMAN 5600
30 all job 9400
all deptno all job 29025
5. use hint
當多表串連很慢時,用ORDERED提示試試,也許會快很多
SELECT /**//*+ ORDERED */*
FROM a, b, c, d
WHERE
