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Tue, 08 Jul 2008 03:55:00 GMT

1.   select * from emp;

    EMPNO ENAME JOB        MGR HIREDATE     SAL COMM DEPTNO
    ----- ------ --------- ---- ----------- ---- ---- -------
    7369 SMITH CLERK     7902 17-DEC-1980 800           20
    7499 ALLEN SALESMAN 7698 20-FEB-1981 1600 300      30
    7521 WARD   SALESMAN 7698 22-FEB-1981 1250 500      30
    7566 JONES MANAGER   7839 02-APR-1981 2975           20
    7654 MARTIN SALESMAN 7698 28-SEP-1981 1250 1400      30
    7698 BLAKE MANAGER   7839 01-MAY-1981 2850           30
    7782 CLARK MANAGER   7839 09-JUN-1981 2450           10
    7788 SCOTT ANALYST   7566 09-DEC-1982 3000           20
    7839 KING   PRESIDENT      17-NOV-1981 5000           10
    7844 TURNER SALESMAN 7698 08-SEP-1981 1500    0      30
    7876 ADAMS CLERK     7788 12-JAN-1983 1100           20
    7900 JAMES CLERK     7698 03-DEC-1981 950           30
    7902 FORD   ANALYST   7566 03-DEC-1981 3000           20
    7934 MILLER CLERK     7782 23-JAN-1982 1300           10

2.问题�Q�查找DEPTNO 20中出现最多次数的工资�Q?/span>
select sal
    from emp
    where deptno = 20
    order by sal

           SAL
    ----------
           800
          1100
          2975
          3000
          3000

3.解决�Ҏ(gu��)��
使用�H�口函数 DENSE_RANK,把工资重复出现的�ơ数分等�U��?br /> 1     select sal
2       from (
3     select sal,
4            dense_rank()over( order by cnt desc) as rnk
5       from (
6     select sal, count(*) as cnt
8       from emp
9      where deptno = 20
10      group by sal
11            ) x
12            ) y
13      where rnk = 1

�q�风舞�?/a> 2008-07-08 11:55 发表评论

SQl中关于空值NULL

Tue, 08 Jul 2008 02:43:00 GMT

1.ISNULL 判断某一字段是否为空�Q�若为空�q�回 TRUE�Q�否则返�?FALSE

2.NULLIF�Q�字�D�名�Q�字�D��|��若字�D�名的��gؓ"字段�?�Q�则��该字段值替换成NULL

3.COALESCE(表达�?�Q�表辑ּ�2�Q?..表达式n�Q?从左到右依次判断表达式的�?�q�回�W�一个非�I�的表达式的倹{�?br />

�q�风舞�?/a> 2008-07-08 10:43 发表评论

Oracle日期函数

Fri, 04 Jul 2008 02:32:00 GMT

Oracle的日期函�?

Oracle�?i开始就提供了大量的日期函数�Q�这些日期函数包括对日期�q�行加减、�{换、截取等功能。下面是Oracle提供的日期函��C��览表

Function	Use
ADD_MONTHS	Adds months to a date
LAST_DAY	Computes the last day of the month
MONTHS_BETWEEN	Determines the number of months between two dates
NEW_TIME	Translates a time to a new time zone
NEXT_DAY	Returns the date of the next specified weekday
ROUND	Rounds a date/time value to a specified element
SYSDATE	Returns the current date and time
TO_CHAR	Converts dates to strings
TO_DATE	Converts strings and numbers to dates
TRUNC	Truncates a date/time value to a specific element

更多详细内容请参考：http://m.tkk7.com/pengpenglin/archive/2008/06/30/211589.html

�q�风舞�?/a> 2008-07-04 10:32 发表评论

Oracle分析函数(�?

Thu, 03 Jul 2008 16:12:00 GMT

Oracle分析函数(�?

1.AVG
功能描述�Q�用于计��一个组和数据窗口内表达式的�q�_��倹{�?br /> SAMPLE�Q�下面的例子中列c_mavg计算员工表中每个员工的��^均薪水报告，该��^均值由当前员工和与之具有相同经理的前一个和后一个三者的�q�_��数得来；

SELECT manager_id, last_name, hire_date, salary,
AVG(salary) OVER (PARTITION BY manager_id ORDER BY hire_date
ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING) AS c_mavg
FROM employees;

MANAGER_ID LAST_NAME HIRE_DATE SALARY C_MAVG
---------- ------------------------- --------- ---------- ----------
100 Kochhar 21-SEP-89 17000 17000
100 De Haan 13-JAN-93 17000 15000
100 Raphaely 07-DEC-94 11000 11966.6667
100 Kaufling 01-MAY-95 7900 10633.3333
100 Hartstein 17-FEB-96 13000 9633.33333
100 Weiss 18-JUL-96 8000 11666.6667
100 Russell 01-OCT-96 14000 11833.3333

2.COUNT
功能描述�Q�对一�l�内发生的事情进行篏�U�计敎ͼ�如果指定*或一些非�I�常敎ͼ�count��对所有行计数�Q�如果指定一个表辑ּ��Q�count�q�回表达式非�I��值的计数�Q�当有相同值出现时�Q�这些相�{�的值都会被�U�_��被计��的��|��可以使用DISTINCT来记录去掉一�l�中完全相同的数据后出现的行数�?br /> SAMPLE�Q�下面例子中计算每个员工在按薪水排序中当前行附近薪水在[n-50,n+150]之间的行敎ͼ�n表示当前行的薪水例如�Q�Philtanker的薪�?200�Q�排在他之前的行中薪水大于等�?200-50的有1行，排在他之后的行中薪水��于�{�于2200�Q?50的行没有�Q�所以count计数值cnt3�?�Q�包括自己当前行�Q�；cnt2值相当于��于�{�于当前行的SALARY值的所有行�?

SELECT last_name, salary, COUNT(*) OVER () AS cnt1,
COUNT(*) OVER (ORDER BY salary) AS cnt2,
COUNT(*) OVER (ORDER BY salary RANGE BETWEEN 50 PRECEDING
AND 150 FOLLOWING) AS cnt3 FROM employees;

LAST_NAME SALARY CNT1 CNT2 CNT3
------------------------- ---------- ---------- ---------- ----------
Olson 2100 107 1 3
Markle 2200 107 3 2
Philtanker 2200 107 3 2
Landry 2400 107 5 8
Gee 2400 107 5 8
Colmenares 2500 107 11 10
Patel 2500 107 11 10

3.DENSE_RANK
功能描述�Q�根据ORDER BY子句中表辑ּ�的��|��从查询返回的每一行，计算它们与其它行的相对位�|�。组内的数据按ORDER BY子句排序�Q�然后给每一行赋一个号�Q�从而�Ş成一个序列，该序列从1开始，往后篏加。每�ơORDER BY表达式的值发生变化时�Q�该序列也随之增加。有同样值的行得到同��L��数字序号�Q�认为null时相�{�的�Q�。密集的序列�q�回的时没有间隔的数
SAMPLE�Q�下例中计算每个员工按部门分区再按薪水排序，依次出现的序列号�Q�注意与RANK函数的区别）

SELECT d.department_id , e.last_name, e.salary, DENSE_RANK()
OVER (PARTITION BY e.department_id ORDER BY e.salary) as drank
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_id IN ('60', '90');

DEPARTMENT_ID LAST_NAME SALARY DRANK
------------- ------------------------- ---------- ----------
60 Lorentz 4200 1
60 Austin 4800 2
60 Pataballa 4800 2
60 Ernst 6000 3
60 Hunold 9000 4
90 Kochhar 17000 1
90 De Haan 17000 1
90 King 24000 2

RANK()与DENSE_RANK()用法相当�Q�但是有一个区别：DENSE_RANK在处理相同的�{��Ӟ��{��的数��g��会蟩�q?RANK()则蟩�q��?br />

RANK
功能描述�Q�根据ORDER BY子句中表辑ּ�的��|��从查询返回的每一行，计算它们与其它行的相对位�|�。组内的数据按ORDER BY子句排序�Q�然后给每一行赋一个号�Q�从而�Ş成一个序列，该序列从1开始，往后篏加。每�ơORDER BY表达式的值发生变化时�Q�该序列也随之增加。有同样值的行得到同��L��数字序号�Q�认为null时相�{�的�Q�。然而，如果两行的确得到同样的排序，则序数将随后跌��。若两行序数�?�Q�则没有序数2�Q�序列将�l�组中的下一行分配�?�Q�DENSE_RANK则没有�Q何蟩跃�?br /> SAMPLE�Q�下例中计算每个员工按部门分区再按薪水排序，依次出现的序列号�Q�注意与DENSE_RANK函数的区别）

SELECT d.department_id , e.last_name, e.salary, RANK()
OVER (PARTITION BY e.department_id ORDER BY e.salary) as drank
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_id IN ('60', '90');

DEPARTMENT_ID LAST_NAME SALARY DRANK
------------- ------------------------- ---------- ----------
60 Lorentz 4200 1
60 Austin 4800 2
60 Pataballa 4800 2
60 Ernst 6000 4
60 Hunold 9000 5
90 Kochhar 17000 1
90 De Haan 17000 1
90 King 24000 3

4.FIRST
功能描述�Q�从DENSE_RANK�q�回的集合中取出排在最前面的一个值的行（可能多行�Q�因为值可能相�{�）�Q�因此完整的语法需要在开始处加上一个集合函��C��从中取出记录SAMPLE.
下面例子中DENSE_RANK按部门分区，再按佣金commission_pct排序�Q�FIRST取出佣金最低的对应的所有行�Q�然后前面的MAX函数从这个集合中取出薪水最低的��|��LAST取出佣金最高的对应的所有行�Q�然后前面的MIN函数从这个集合中取出薪水最高的�?
SELECT last_name, department_id, salary,
MIN(salary) KEEP (DENSE_RANK FIRST ORDER BY commission_pct)
OVER (PARTITION BY department_id) "Worst",
MAX(salary) KEEP (DENSE_RANK LAST ORDER BY commission_pct)
OVER (PARTITION BY department_id) "Best"
FROM employees
WHERE department_id in (20,80)
ORDER BY department_id, salary;

LAST_NAME DEPARTMENT_ID SALARY Worst Best
------------------------- ------------- ---------- ---------- ----------
Fay 20 6000 6000 13000
Hartstein 20 13000 6000 13000
Kumar 80 6100 6100 14000
Banda 80 6200 6100 14000
Johnson 80 6200 6100 14000
Ande 80 6400 6100 14000
Lee 80 6800 6100 14000
Tuvault 80 7000 6100 14000
Sewall 80 7000 6100 14000
Marvins 80 7200 6100 14000
Bates 80 7300 6100 14000

5.FIRST_VALUE
功能描述�Q�返回组中数据窗口的�W�一个倹{�?br /> SAMPLE�Q�下面例子计��按部门分区按薪水排序的数据�H�口的第一个值对应的名字�Q�如果薪水的�W�一个值有多个�Q�则从多个对应的名字中取�~�省排序的第一个名�?

SELECT department_id, last_name, salary, FIRST_VALUE(last_name)
OVER (PARTITION BY department_id ORDER BY salary ASC ) AS lowest_sal
FROM employees
WHERE department_id in(20,30);

DEPARTMENT_ID LAST_NAME SALARY LOWEST_SAL
------------- ------------------------- ---------- --------------
20 Fay 6000 Fay
20 Hartstein 13000 Fay
30 Colmenares 2500 Colmenares
30 Himuro 2600 Colmenares
30 Tobias 2800 Colmenares
30 Baida 2900 Colmenares
30 Khoo 3100 Colmenares
30 Raphaely 11000 Colmenares

6.LAST
功能描述�Q�从DENSE_RANK�q�回的集合中取出排在最后面的一个值的行（可能多行�Q�因为值可能相�{�）�Q�因此完整的语法需要在开始处加上一个集合函��C��从中取出记录
SAMPLE�Q�下面例子中DENSE_RANK按部门分区，再按佣金commission_pct排序�Q�FIRST取出佣金最低的对应的所有行�Q�然后前面的MAX函数从这个集合中取出薪水最低的��|��LAST取出佣金最高的对应的所有行�Q�然后前面的MIN函数从这个集合中取出薪水最高的�?br /> SELECT last_name, department_id, salary,
MIN(salary) KEEP (DENSE_RANK FIRST ORDER BY commission_pct)
OVER (PARTITION BY department_id) "Worst",
MAX(salary) KEEP (DENSE_RANK LAST ORDER BY commission_pct)
OVER (PARTITION BY department_id) "Best"
FROM employees
WHERE department_id in (20,80)
ORDER BY department_id, salary;

7.LAST_VALUE
功能描述�Q�返回组中数据窗口的最后一个倹{�?br /> SAMPLE�Q�下面例子计��按部门分区按薪水排序的数据�H�口的最后一个值对应的名字�Q�如果薪水的最后一个值有多个�Q�则从多个对应的名字中取�~�省排序的最后一个名�?br /> SELECT department_id, last_name, salary, LAST_VALUE(last_name)
OVER(PARTITION BY department_id ORDER BY salary) AS highest_sal
FROM employees
WHERE department_id in(20,30);

DEPARTMENT_ID LAST_NAME SALARY HIGHEST_SAL
------------- ------------------------- ---------- ------------
20 Fay 6000 Fay
20 Hartstein 13000 Hartstein
30 Colmenares 2500 Colmenares
30 Himuro 2600 Himuro
30 Tobias 2800 Tobias
30 Baida 2900 Baida
30 Khoo 3100 Khoo
30 Raphaely 11000 Raphaely

8.LAG
功能描述�Q�可以访问结果集中的其它行而不用进行自�q�接。它允许��d��理游标，��好像游标是一个数�l�一栗��在�l�定�l�中可参考当前行之前的行�Q�这样就可以从组中与当前行一起选择以前的行。Offset是一个正整数�Q�其默认��gؓ1�Q�若索引��出�H�口的范��_��p��回默认��|��默认�q�回的是�l�中�W�一行）�Q�其相反的函数是LEAD
SAMPLE�Q�下面的例子中列prev_sal�q�回按hire_date排序的前1行的salary�?

SELECT last_name, hire_date, salary,
LAG(salary, 1, 0) OVER (ORDER BY hire_date) AS prev_sal
FROM employees
WHERE job_id = 'PU_CLERK';

LAST_NAME HIRE_DATE SALARY PREV_SAL
------------------------- ---------- ---------- ----------
Khoo 18-5�?-95 3100 0
Tobias 24-7�?-97 2800 3100
Baida 24-12�?97 2900 2800
Himuro 15-11�?98 2600 2900
Colmenares 10-8�?-99 2500 2600

9.LEAD
功能描述�Q�LEAD与LAG相反�Q�LEAD可以讉K��l�中当前行之后的行。Offset是一个正整数�Q�其默认��gؓ1�Q�若索引��出�H�口的范��_��p��回默认��|��默认�q�回的是�l�中�W�一行）
SAMPLE�Q�下面的例子中每行的"NextHired"�q�回按hire_date排序的下一行的hire_date�?

SELECT last_name, hire_date,
LEAD(hire_date, 1) OVER (ORDER BY hire_date) AS "NextHired"
FROM employees WHERE department_id = 30;

LAST_NAME HIRE_DATE NextHired
------------------------- --------- ---------
Raphaely 07-DEC-94 18-MAY-95
Khoo 18-MAY-95 24-JUL-97
Tobias 24-JUL-97 24-DEC-97
Baida 24-DEC-97 15-NOV-98
Himuro 15-NOV-98 10-AUG-99
Colmenares 10-AUG-99

10.SUM
功能描述�Q�该函数计算�l�中表达式的累积和�?br /> SAMPLE�Q�下例计��同一�l�理下员工的薪水累积�?

SELECT manager_id, last_name, salary,
SUM (salary) OVER (PARTITION BY manager_id ORDER BY salary
RANGE UNBOUNDED PRECEDING) l_csum
FROM employees
WHERE manager_id in (101,103,108);

MANAGER_ID LAST_NAME SALARY L_CSUM
---------- ------------------------- ---------- ----------
101 Whalen 4400 4400
101 Mavris 6500 10900
101 Baer 10000 20900
101 Greenberg 12000 44900
101 Higgins 12000 44900
103 Lorentz 4200 4200
103 Austin 4800 13800
103 Pataballa 4800 13800
103 Ernst 6000 19800
108 Popp 6900 6900
108 Sciarra 7700 14600
108 Urman 7800 22400
108 Chen 8200 30600
108 Faviet 9000 39600

11.MAX
功能描述�Q�在一个组中的数据�H�口中查找表辑ּ�的最大倹{�?br /> SAMPLE�Q�下面例子中dept_max�q�回当前行所在部门的最大薪水�?

SELECT department_id, last_name, salary,
MAX(salary) OVER (PARTITION BY department_id) AS dept_max
FROM employees WHERE department_id in (10,20,30);

DEPARTMENT_ID LAST_NAME SALARY DEPT_MAX
------------- ------------------------- ---------- ----------
10 Whalen 4400 4400
20 Hartstein 13000 13000
20 Fay 6000 13000
30 Raphaely 11000 11000
30 Khoo 3100 11000
30 Baida 2900 11000
30 Tobias 2800 11000
30 Himuro 2600 11000
30 Colmenares 2500 11000

12.MIN
功能描述�Q�在一个组中的数据�H�口中查找表辑ּ�的最��倹{�?br /> SAMPLE�Q�下面例子中dept_min�q�回当前行所在部门的最��薪水�?

SELECT department_id, last_name, salary,
MIN(salary) OVER (PARTITION BY department_id) AS dept_min
FROM employees WHERE department_id in (10,20,30);

DEPARTMENT_ID LAST_NAME SALARY DEPT_MIN
------------- ------------------------- ---------- ----------
10 Whalen 4400 4400
20 Hartstein 13000 6000
20 Fay 6000 6000
30 Raphaely 11000 2500
30 Khoo 3100 2500
30 Baida 2900 2500
30 Tobias 2800 2500
30 Himuro 2600 2500
30 Colmenares 2500 2500

�q�风舞�?/a> 2008-07-04 00:12 发表评论

Thu, 03 Jul 2008 16:10:00 GMT

�H�口函数
      Oracle�?.1.6开始提供分析函敎ͼ�分析函数用于计算��Z��l�的某种聚合��|��它和聚合函数的不同之处是对于每个�l�返回多行，而聚合函数对于每个组只返回一行�?br />     开�H�函数指定了分析函数工作的数据窗口大��，�q�个数据�H�口大小可能会随着行的变化而变化，举例如下�Q?br /> 1) over(order by salary)
     按照salary排序�q�行累计�Q�order by是个默认的开�H�函�?br /> 2) over(partition by deptno)
    按照部门分区
3) over(order by salary range between 50 preceding and 150 following)
     每行对应的数据窗口是之前行幅度��g��过50�Q�之后行�q�度��g��过150
4) over(order by salary rows between 50 preceding and 150 following)
    每行对应的数据窗口是之前50行，之后150�?br /> 5) over(order by salary rows between unbounded preceding and unbounded following)
    每行对应的数据窗口是从第一行到最后一行，�{�效�Q?br />     over(order by salary range between unbounded preceding and unbounded following)

�q�风舞�?/a> 2008-07-04 00:10 发表评论

Thu, 03 Jul 2008 15:08:00 GMT

1.MySQL
    同时使用内置RAND函数、LIMIT函数和ORDER BY
        select * from table
            order by rand() limit 5
2.Oracle
    同时使用DBMS_RANDOM包中的内�|�函�?VALUE�?ORDER BY和内�|�函数ROWNUM
       select * from(
           select name from table order by dbms_random.value()
       ) where rownum <=5

�q�风舞�?/a> 2008-07-03 23:08 发表评论

Thu, 03 Jul 2008 14:59:00 GMT

1.Oracle
    对天数采用标准加减，使用ADD_MONTHS函数加减月数和年�?/p>    例如 1)insertDate是数据库表中的一个日期类型的字段
             �?insertDate-5为前五天�Q�同理insertDate+5为后五天
             2) 若要获得前一个月的时��_��?add_months(insertDate,-1);
                 若要获得后一个月的时��_��?add_months(insertDate,1)
             3)若要获得前一�q�的旉��Q�则 add_months(insetDate,-1*12)
                 若要获得后一�q�的旉��Q�则 add_months(insetDate, 1*12)
2.MySQL
      同时使用标准加减和INTERVAL关键字，INTEVRAL 指定旉��单位
   例如�Q�insertDate - INTERVAL 1 day
               insertDate + INTERVAL 1 day
               insertDate - INTERVAL 1 month
               insertDate - INTERVAL 1 year
      也可使用DATE_ADD(),ADDDATE(),SUBDATE()函数
              DATE_ADD(insertDate,INTERVAL 5 day)
              DATE_ADD(insertDate,INTERVAL -5 day)
              ADDDATE(),SUBDATE() 使用�Ҏ(gu��)��c�M��

�q�风舞�?/a> 2008-07-03 22:59 发表评论