Oracle高级查询

使用Oracle特有的查询语法, 可以达到事半功倍的效果

1. 树查询

create table tree (

id number(10) not null primary key,

name varchar2(100) not null,

super number(10) not null // 0 is root

);

-- 从子到父

select * from tree start with id = ? connect by id = prior super

-- 从父到子

select * from tree start with id = ? connect by prior id = super

-- 整棵树

select * from tree start with super = 0 connect by prior id = super

2. 分页查询

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. 累加查询, 以scott.emp为例

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. 高级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

当多表连接很慢时,用ORDERED提示试试,也许会快很多

FROM a, b, c, d

WHERE