[20170525]分析函式first_value.txt

[20170525]分析函式first_value.txt

--//昨天看sql語句,發現居然分析函式first_value.我一直認為開發如果要做一些報表需要了解學習一些oracle分析函式的知識,我發現許
--//多開發這方面一篇空白.我曾經更開發講過,為什麼自己不會一點點看書,僅僅1,2天有個大概記憶,以後在baidu,google查詢就ok了.
--//可惜遇到這樣的問題還是寫出一些變態的sql語句,無語!!
--//透過例子說明:

1.環境:

SCOTT@book> @ &r/ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

SCOTT@book> select emp.*,first_value(sal) over (partition by deptno order by sal desc) deptmax_sal  from emp ;
     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO DEPTMAX_SAL
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- -----------
      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10        5000
      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10        5000
      7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10        5000
      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20        3000
      7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20        3000
      7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20        3000
      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20        3000
      7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20        3000
      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30        2850
      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30        2850
      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30        2850
      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30        2850
      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30        2850
      7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30        2850
14 rows selected.

--//這樣可以查詢部門最高工資.我以前一般這樣寫.

SCOTT@book> select emp.*,max(sal) over (partition by deptno order by sal desc) deptmax_sal  from emp ;
     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO DEPTMAX_SAL
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- -----------
      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10        5000
      7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10        5000
      7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10        5000
      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20        3000
      7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20        3000
      7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20        3000
      7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20        3000
      7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20        3000
      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30        2850
      7499 ALLEN      SALESMAN        7698 1981-02-20 00:00:00       1600        300         30        2850
      7844 TURNER     SALESMAN        7698 1981-09-08 00:00:00       1500          0         30        2850
      7654 MARTIN     SALESMAN        7698 1981-09-28 00:00:00       1250       1400         30        2850
      7521 WARD       SALESMAN        7698 1981-02-22 00:00:00       1250        500         30        2850
      7900 JAMES      CLERK           7698 1981-12-03 00:00:00        950                    30        2850
14 rows selected.

--//使用first_value分析函式的好處可以顯示別的欄位,不一定是sal.
--//比如要查詢顯示每個部門工資最高的記錄.

SCOTT@book> select * from (select emp.*,first_value(empno) over (partition by deptno order by sal desc) maxsal_empno  from emp ) where empno=MAXSAL_EMPNO;
     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO MAXSAL_EMPNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- ------------
      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10         7839
      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20         7788
      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30         7698

--//我以前的寫法存在一些問題,如下:
SCOTT@book> select * from (select emp.*,max(sal) over (partition by deptno order by sal desc) maxsal  from emp ) where sal=MAXSAL;
     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO     MAXSAL
---------- ---------- --------- ---------- ------------------- ---------- ---------- ---------- ----------
      7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10       5000
      7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20       3000
      7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20       3000
      7698 BLAKE      MANAGER         7839 1981-05-01 00:00:00       2850                    30       2850

--//這樣查詢部門deptno=20有2條記錄.當然還有許多寫法,總之開發應該抽一點點時間學習一些分析函式知識.