In this mini-lesson, learn how to use the ANSI syntax for pagination style queries with the FETCH FIRST and OFFSET clauses

1. 1
12c

2. 2
the focus ...
the day to day stuff

3. Feature
top-n simplifications
3

4. "5 most recently hired employees"
4

5. SQL> select empno, ename, hiredate
2 from scott.emp
3 where rownum <= 5
4 order by hiredate desc;
EMPNO ENAME HIREDATE
---------- ---------- -------------------
7654 MARTIN 28/09/1981 00:00:00
7566 JONES 02/04/1981 00:00:00
7521 WARD 22/02/1981 00:00:00
7499 ALLEN 20/02/1981 00:00:00
7369 SMITH 17/12/1980 00:00:00
5

6. inline view
6

7. SQL> select *
2 from (
3 select empno, ename, hiredate
4 from scott.emp
5 order by hiredate desc
6 )
7 where rownum <= 2;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7876 ADAMS 23-MAY-87
7788 SCOTT 19-APR-87
7

8. ------------------------------------------------
| Id | Operation | Name | Rows |
------------------------------------------------
| 0 | SELECT STATEMENT | | 2 |
|* 1 | COUNT STOPKEY | | |
| 2 | VIEW | | 14 |
|* 3 | SORT ORDER BY STOPKEY| | 14 |
| 4 | TABLE ACCESS FULL | EMP | 14 |
------------------------------------------------
8

9. SQL> select *
2 from (
3 select
4 empno, ename, hiredate,
5 row_number() over ( order by hiredate desc) rn
6 from scott.emp
7 )
8 where rn <= 2;
9

10. -------------------------------------------------
| Id | Operation | Name | Rows |
-------------------------------------------------
| 0 | SELECT STATEMENT | | 14 |
|* 1 | VIEW | | 14 |
|* 2 | WINDOW SORT PUSHED RANK| | 14 |
| 3 | TABLE ACCESS FULL | EMP | 14 |
-------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RN"<=2)
2 - filter(ROW_NUMBER() OVER
( ORDER BY HIREDATE") DESC )<=2)
10

11. and never this !
11

12. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
<fetch fetch fetch ... >
12

13. ------------------------------------------------
| Id | Operation | Name | Rows |
------------------------------------------------
| 0 | SELECT STATEMENT | | 2 |
|* 1 | SORT ORDER BY | | 14 |
| 2 | TABLE ACCESS FULL | EMP | 14 |
------------------------------------------------
13

14. tid bit
14

15. SQL> select /*+ FIRST_ROWS(10) */ *
2 from (
3 select empno, ename, hiredate
4 from scott.emp
5 order by hiredate desc
6 )
7 where rownum <= 2;
15

16. 12c .... "easier"
16

17. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 fetch first 2 rows only;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7876 ADAMS 23-MAY-87
7788 SCOTT 19-APR-87
17

18. behind the scenes
18

19. -------------------------------------------------
| Id | Operation | Name | Rows |
-------------------------------------------------
| 0 | SELECT STATEMENT | | 14 |
|* 1 | VIEW | | 14 |
|* 2 | WINDOW SORT PUSHED RANK| | 14 |
| 3 | TABLE ACCESS FULL | EMP | 14 |
-------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("from$_subquery$_002".
"rowlimit_$$_rownumber"<=2)
2 - filter(ROW_NUMBER() OVER
( ORDER BY HIREDATE") DESC )<=2)
19

20. variations
20

21. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 fetch first 1 row only;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7876 ADAMS 23-MAY-87
21

22. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 fetch first 5 row only;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7876 ADAMS 23-MAY-87
7788 SCOTT 19-APR-87
7934 MILLER 23-JAN-82
7900 JAMES 03-DEC-81
7902 FORD 03-DEC-81
22

23. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 fetch first 10 percent rows only;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7876 ADAMS 23-MAY-87
7788 SCOTT 19-APR-87
23

24. pagination
24

25. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 offset 5 rows fetch next 3 rows only;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7839 KING 17-NOV-81
7654 MARTIN 28-SEP-81
7844 TURNER 08-SEP-81
25

26. idiosyncracies
26

27. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 fetch LAST 5 rows only;
fetch LAST 5 rows only
*
ERROR at line 4:
ORA-00905: missing keyword
27

28. SQL> select *
2 from (
3 select empno, ename, hiredate
4 from scott.emp
5 order by hiredate asc
6 fetch first 5 rows only
7 )
8 order by hiredate desc;
EMPNO ENAME HIREDATE
---------- ---------- ---------
7698 BLAKE 01-MAY-81
7566 JONES 02-APR-81
7521 WARD 22-FEB-81
7499 ALLEN 20-FEB-81
7369 SMITH 17-DEC-80 28

29. no percent pagination
29

30. SQL> select empno, ename, hiredate
2 from scott.emp
3 order by hiredate desc
4 offset 20 percent fetch
5 next 10 percent rows only;
offset 20 percent fetch next 10 percent rows only
*
ERROR at line 4:
ORA-00905: missing keyword
30