分类： Oracle
2012-06-26 15:20:13
oracle中row_number() OVER (PARTITION BY COL1 ORDER BY COL2)
row_number() OVER (PARTITION BY COL1 ORDER BY COL2) 表示根据COL1分组，在分组内部根据 COL2排序，而此函数计算的值就表示每组内部排序后的顺序编号（组内连续的唯一的).
与rownum的区别在于：使用rownum进行排序的时候是先对结果集加入伪列rownum然后再进行排序，而此函数在包含排序从句后是先排序再计算行号码．
row_number()和rownum差不多，功能更强一点（可以在各个分组内从1开时排序）．
rank()是跳跃排序，有两个第二名时接下来就是第四名（同样是在各个分组内）．
dense_rank()是连续排序，有两个第二名时仍然跟着第三名。相比之下row_number是没有重复值的 ．
lag（arg1,arg2,arg3):
arg1是从其他行返回的表达式
arg2是希望检索的当前行分区的偏移量。1是一个正的偏移量，是一个往回检索以前的行的数目。
arg3是在arg2表示的数目超出了分组的范围时返回的值。
看几个语句:
语句一:
select row_number() over(order by sale/cnt desc) as sort, sale/cnt
from (
select -60 as sale,3 as cnt from dual union
select 24 as sale,6 as cnt from dual union
select 50 as sale,5 as cnt from dual union
select -20 as sale,2 as cnt from dual union
select 40 as sale,8 as cnt from dual);
执行结果:
SORT SALE/CNT
---------- ----------
1 10
2 5
3 4
4 -10
5 -20
语句二:查询员工的工资,按部门排序
select ename,sal,row_number() over (partition by deptno order by sal desc) as sal_order from scott.emp;
执行结果:
ENAME SAL SAL_ORDER
-------------------- ---------- ----------
KING 5000 1
CLARK 2450 2
MILLER 1300 3
SCOTT 3000 1
FORD 3000 2
JONES 2975 3
ADAMS 1100 4
SMITH 800 5
BLAKE 2850 1
ALLEN 1600 2
TURNER 1500 3
WARD 1250 4
MARTIN 1250 5
JAMES 950 6
已选择14行。
语句三:查询每个部门的最高工资
select deptno,ename,sal from
(select deptno,ename,sal,row_number() over (partition by deptno order by sal desc) as sal_order
from scott.emp) where sal_order <2;
执行结果:
DEPTNO ENAME SAL
---------- -------------------- ----------
10 KING 5000
20 SCOTT 3000
30 BLAKE 2850
已选择3行。
语句四：
select deptno,sal,rank() over (partition by deptno order by sal) as rank_order from scott.emp order by deptno;
执行结果:
DEPTNO SAL RANK_ORDER
---------- ---------- ----------
10 1300 1
10 2450 2
10 5000 3
20 800 1
20 1100 2
20 2975 3
20 3000 4
20 3000 4
30 950 1
30 1250 2
30 1250 2
30 1500 4
30 1600 5
30 2850 6
已选择14行。
语句五：
select deptno,sal,dense_rank() over(partition by deptno order by sal) as dense_rank_order from scott.emp order by deptn;
执行结果：
DEPTNO SAL DENSE_RANK_ORDER
---------- ---------- ----------------
10 1300 1
10 2450 2
10 5000 3
20 800 1
20 1100 2
20 2975 3
20 3000 4
20 3000 4
30 950 1
30 1250 2
30 1250 2
30 1500 3
30 1600 4
30 2850 5
已选择14行。
语句六：
select deptno,ename,sal,lag(ename,1,null) over(partition by deptno order by ename) as lag_ from scott.emp order by deptno;
执行结果：
DEPTNO ENAME SAL LAG_
---------- -------------------- ---------- --------------------
10 CLARK 2450
10 KING 5000 CLARK
10 MILLER 1300 KING
20 ADAMS 1100
20 FORD 3000 ADAMS
20 JONES 2975 FORD
20 SCOTT 3000 JONES
20 SMITH 800 SCOTT
30 ALLEN 1600
30 BLAKE 2850 ALLEN
30 JAMES 950 BLAKE
30 MARTIN 1250 JAMES
30 TURNER 1500 MARTIN
30 WARD 1250 TURNER
已选择14行。
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再看几个例子：
语法格式:
1.row_number() over (order by col_1[,col_2 ...])
作用:按照col_1[,col_2 ...]排序,返回排序后的结果集，
此用法有点像rownum,为每一行返回一个不相同的值：
select rownum,ename,job,
row_number() over (order by rownum) row_number
from emp;
ROWNUM ENAME JOB ROW_NUMBER
---------- ---------- --------- ----------
1 SMITH CLERK 1
2 ALLEN SALESMAN 2
3 WARD SALESMAN 3
4 JONES MANAGER 4
5 MARTIN SALESMAN 5
6 BLAKE MANAGER 6
7 CLARK MANAGER 7
8 SCOTT ANALYST 8
9 KING PRESIDENT 9
10 TURNER SALESMAN 10
11 ADAMS CLERK 11
12 JAMES CLERK 12
13 FORD ANALYST 13
14 MILLER CLERK 14
如果没有partition by子句, 结果集将是按照order by 指定的列进行排序；
with row_number_test as(
select 22 a,'twenty two' b from dual union all
select 1,'one' from dual union all
select 13,'thirteen' from dual union all
select 5,'five' from dual union all
select 4,'four' from dual)
select a,b,
row_number() over (order by b)
from row_number_test
order by a;
正如我们所期待的,row_number()返回按照b列排序的结果,
然后再按照a进行排序,才得到下面的结果:
A B ROW_NUMBER()OVER(ORDERBYB)
-- ---------- --------------------------
1 one 3
4 four 2
5 five 1
13 thirteen 4
22 twenty two 5
2.row_number() over (partition by col_n[,col_m ...] order by col_1[,col_2 ...])
作用:先按照col_n[,col_m ...进行分组,
再在每个分组中按照col_1[,col_2 ...]进行排序(升序),
最后返回排好序后的结果集:
with row_number_test as(
select 22 a,'twenty two' b,'*' c from dual union all
select 1,'one','+' from dual union all
select 13,'thirteen','*' from dual union all
select 5,'five','+' from dual union all
select 4,'four','+' from dual)
select a,b,
row_number() over (partition by c order by b) row_number
from row_number_test
order by a;
这个例子中，我们先按照c列分组，分为2组('*'组,'+'组)，
再按照每个小组的b列进行排序(按字符串首字母的ascii码排),
最后按照a列排序,得到下面的结果集:
A B ROW_NUMBER
-- ---------- ----------
1 one 3
4 four 2
5 five 1
13 thirteen 1
22 twenty two 2
-------------------------------------------------------------------------------
统计每个字段(以各字段分组)中有多少记录的优化语句：
select count(1)
from
(
select row_number() over(partition by c1,c2,c3,c4,c5 order by c1) rw
from t1
)
where rw=1
