ORACLE有几个函数专门用来产生伪列的,rownum,rowid,row_number(),rank,dense_rank,lan
样表:
SQL> select * from stu_score;
STU_NO SUB_NO SCORE
---------- ---------- ----------
1 1 99
2 1 98
3 1 100
4 2 88
5 2 87
6 2 88
7 3 99
8 3 88
9 3 100
9 rows selected.
rownum按行的顺序自动增加产生
SQL> select rownum, stu_score.* from stu_score;
ROWNUM STU_NO SUB_NO SCORE
---------- ---------- ---------- ----------
1 1 1 99
2 2 1 98
3 3 1 100
4 4 2 88
5 5 2 87
6 6 2 88
7 7 3 99
8 8 3 88
9 9 3 100
9 rows selected.
rowid内部ID号,这个是真正存在表中的
SQL> select rownum from dual connect by rownum<10;
ROWNUM
----------
1
2
3
4
5
6
7
8
9
10
10 rows selected.
这个是一个比较有用的语句
SQL> select to_date('2006-03-31','yyyy-mm-dd')+rownum rn from dual connect by ro
wnum < 10;
RN
--------------
01-4月 -06
02-4月 -06
03-4月 -06
04-4月 -06
05-4月 -06
06-4月 -06
07-4月 -06
08-4月 -06
09-4月 -06
10-4月 -06
10 rows selected.
SQL> select rowid, stu_score.* from stu_score;
ROWID STU_NO SUB_NO SCORE
------------------ ---------- ---------- ----------
AAAMGBAAQAAAEdqAAA 1 1 99
AAAMGBAAQAAAEdqAAB 2 1 98
AAAMGBAAQAAAEdqAAC 3 1 100
AAAMGBAAQAAAEdqAAD 4 2 88
AAAMGBAAQAAAEdqAAE 5 2 87
AAAMGBAAQAAAEdqAAF 6 2 88
AAAMGBAAQAAAEdqAAG 7 3 99
AAAMGBAAQAAAEdqAAH 8 3 88
AAAMGBAAQAAAEdqAAI 9 3 100
9 rows selected.
给每个组内的不同记录进行排号,如果要查询每门课程成绩的前两名的记录,就可以用这个实现
SQL> SELECT stu_no,sub_no,score,row_number() over(PARTITION BY sub_no ORDER BY s
core DESC) rn FROM stu_score
2 ;
STU_NO SUB_NO SCORE RN
---------- ---------- ---------- ----------
3 1 100 1
1 1 99 2
2 1 98 3
4 2 88 1
6 2 88 2
5 2 87 3
9 3 100 1
7 3 99 2
8 3 88 3
9 rows selected.
SQL> select * from
2 (SELECT stu_no,sub_no,score,row_number() over(PARTITION BY sub_no ORDER BY
score DESC) rn FROM stu_score)
3 WHERE rn<3;
STU_NO SUB_NO SCORE RN
---------- ---------- ---------- ----------
3 1 100 1
1 1 99 2
4 2 88 1
6 2 88 2
9 3 100 1
7 3 99 2
6 rows selected.
与上面类似,略与不同,一看就知道了
SQL> SELECT stu_no,sub_no,score,RANK() over(PARTITION BY sub_no ORDER BY score D
ESC) rn FROM stu_score
2 ;
STU_NO SUB_NO SCORE RN
---------- ---------- ---------- ----------
3 1 100 1
1 1 99 2
2 1 98 3
4 2 88
1 6 2 88
1 5 2 87
3 9 3 100 1
7 3 99 2
8 3 88 3
9 rows selected.
与RANK类似,可以看出区别来
SQL> SELECT stu_no,sub_no,score,dense_RANK() over(PARTITION BY sub_no ORDER BY s
core DESC) rn FROM stu_score;
STU_NO SUB_NO SCORE RN
---------- ---------- ---------- ----------
3 1 100 1
1 1 99 2
2 1 98 3
4 2 88
1 6 2 88
1 5 2 87
2
9 3 100 1
7 3 99 2
8 3 88 3
9 rows selected.
对列进行偏移
SQL> SELECT stu_no,sub_no,score,lag(score,1,null) over(PARTITION BY sub_no ORDER
BY score DESC) rn FROM stu_score
2 ;
STU_NO SUB_NO SCORE RN
---------- ---------- ---------- ----------
3 1 100
1 1 99 100
2 1 98 99
4 2 88
6 2 88 88
5 2 87 88
9 3 100
7 3 99 100
8 3 88 99
9 rows selected.
判断)
:检查发运网络.sql)
