国产精品久久久久久久一区探花,在线观看精品自拍私拍,亚洲精品一区二区在线播放∴

koradji — Wed, 18 Apr 2012 06:46:00 GMT

1. 打开重复记录的单个字�D�：
select distinct name from table
2. 打开重复记录的所有字�D��|��
select * from table where fid in(select min(fid) from table group by name)
假定�Q�name字段包含重复�?br />3. 打开重复��L��ơ数的所有记录：
select * from table where name in(select name from table group by name having count(name)=1)

koradji 2012-04-18 14:46 发表评论

koradji — Mon, 09 Nov 2009 06:04:00 GMT

Correlated Subqueries
A subquery that is allowed to refer to any of the previously mentioned tables is known as a correlated subquery. We also say that the subquery has a correlated reference to a table in the main query.

The following example uses an uncorrelated subquery to list the employee number and name of employees in department 'A00' with a salary greater than the average salary of the department:

     SELECT EMPNO, LASTNAME
        FROM EMPLOYEE
        WHERE WORKDEPT = 'A00'
          AND SALARY > (SELECT AVG(SALARY)
                           FROM EMPLOYEE
                           WHERE WORKDEPT = 'A00')

This statement produces the following result:

EMPNO LASTNAME
------ ---------------
000010 HAAS
000110 LUCCHESSI

If you want to know the average salary for every department, the subquery needs to be evaluated once for every department. You can do this through the correlation capability of SQL, which permits you to write a subquery that is executed repeatedly, once for each row of the table identified in the outer-level query.

The following example uses a correlated subquery to list all the employees whose salary is higher than the average salary of their department:

     SELECT E1.EMPNO, E1.LASTNAME, E1.WORKDEPT
        FROM EMPLOYEE E1
        WHERE SALARY > (SELECT AVG(SALARY)
                           FROM EMPLOYEE E2
                           WHERE E2.WORKDEPT = E1.WORKDEPT)
        ORDER BY E1.WORKDEPT

In this query, the subquery is evaluated once for every department. The result is:

     EMPNO LASTNAME        WORKDEPT
     ------ --------------- --------
     000010 HAAS            A00
     000110 LUCCHESSI       A00
     000030 KWAN            C01
     000060 STERN           D11
     000150 ADAMSON         D11
     000170 YOSHIMURA       D11
     000200 BROWN           D11
     000220 LUTZ            D11
     000070 PULASKI         D21
     000240 MARINO          D21
     000270 PEREZ           D21
     000090 HENDERSON       E11
     000280 SCHNEIDER       E11
     000100 SPENSER         E21
     000330 LEE             E21
     000340 GOUNOT          E21

To write a query with a correlated subquery, use the same basic format of an ordinary outer query with a subquery. However, in the FROM clause of the outer query, just after the table name, place a correlation name. The subquery may then contain column references qualified by the correlation name. For example, if E1 is a correlation name, then E1.WORKDEPT means the WORKDEPT value of the current row of the table in the outer query. The subquery is (conceptually) reevaluated for each row of the table in the outer query.

By using a correlated subquery, you let the system do the work for you and reduce the amount of code you need to write within your application.

Unqualified correlated references are allowed in DB2. For example, the table EMPLOYEE has a column named LASTNAME, but the table SALES has a column named SALES_PERSON, and no column named LASTNAME.

     SELECT LASTNAME, FIRSTNME, COMM
        FROM EMPLOYEE
        WHERE 3 > (SELECT AVG(SALES)
                      FROM SALES
                      WHERE LASTNAME = SALES_PERSON)

In this example, the system checks the innermost FROM clause for a LASTNAME column. Not finding one, it then checks the next innermost FROM clause (which in this case is the outer FROM clause). While not always necessary, qualifying correlated references is recommended to improve the readability of the query and to ensure that you are getting the result that you intend.

Implementing a Correlated Subquery
When would you want to use a correlated subquery? The use of a column function is sometimes a clue.

Let's say you want to list the employees whose level of education is higher than the average for their department.

First, you must determine the select-list items. The problem says "List the employees". This implies that LASTNAME from the EMPLOYEE table should be sufficient to uniquely identify employees. The problem also states the level of education (EDLEVEL) and the employees' departments (WORKDEPT) as conditions. While the problem does not explicitly ask for columns to be displayed, including them in the select-list will help illustrate the solution. A part of the query can now be constructed:

SELECT LASTNAME, WORKDEPT, EDLEVEL
FROM EMPLOYEE

Next, a search condition (WHERE clause) is needed. The problem statement says, "...whose level of education is higher than the average for that employee's department". This means that for every employee in the table, the average education level for that employee's department must be computed. This statement fits the description of a correlated subquery. Some unknown property (the average level of education of the current employee's department) is being computed for each row. A correlation name is needed for the EMPLOYEE table:

SELECT LASTNAME, WORKDEPT, EDLEVEL
FROM EMPLOYEE E1

The subquery needed is simple. It computes the average level of education for each department. The complete SQL statement is:

     SELECT LASTNAME, WORKDEPT, EDLEVEL
        FROM EMPLOYEE E1
        WHERE EDLEVEL > (SELECT AVG(EDLEVEL)
                            FROM EMPLOYEE E2
                            WHERE E2.WORKDEPT = E1.WORKDEPT)

The result is:

     LASTNAME        WORKDEPT EDLEVEL
     --------------- -------- -------
     HAAS            A00           18
     KWAN            C01           20
     PULASKI         D21           16
     HENDERSON       E11           16
     LUCCHESSI       A00           19
     PIANKA          D11           17
     SCOUTTEN        D11           17
     JONES           D11           17
     LUTZ            D11           18
     MARINO          D21           17
     JOHNSON         D21           16
     SCHNEIDER       E11           17
     MEHTA           E21           16
     GOUNOT          E21           16

Suppose that instead of listing the employee's department number, you list the department name. The information you need (DEPTNAME) is in a separate table (DEPARTMENT). The outer-level query that defines a correlation variable can also be a join query (see Selecting Data from More Than One Table for details).

When you use joins in an outer-level query, list the tables to be joined in the FROM clause, and place the correlation name next to the appropriate table name.

To modify the query to list the department's name instead of its number, replace WORKDEPT by DEPTNAME in the select-list. The FROM clause must now also include the DEPARTMENT table, and the WHERE clause must express the appropriate join condition.

This is the modified query:

     SELECT LASTNAME, DEPTNAME, EDLEVEL
        FROM EMPLOYEE E1, DEPARTMENT
        WHERE E1.WORKDEPT = DEPARTMENT.DEPTNO
        AND EDLEVEL > (SELECT AVG(EDLEVEL)
                          FROM EMPLOYEE E2
                          WHERE E2.WORKDEPT = E1.WORKDEPT)

This statement produces the following result:

LASTNAME        DEPTNAME                      EDLEVEL
--------------- ----------------------------- -------
HAAS            SPIFFY COMPUTER SERVICE DIV.       18
LUCCHESSI       SPIFFY COMPUTER SERVICE DIV.       19
KWAN            INFORMATION CENTER                 20
PIANKA          MANUFACTURING SYSTEMS              17
SCOUTTEN        MANUFACTURING SYSTEMS              17
JONES           MANUFACTURING SYSTEMS              17
LUTZ            MANUFACTURING SYSTEMS              18
PULASKI         ADMINISTRATION SYSTEMS             16
MARINO          ADMINISTRATION SYSTEMS             17
JOHNSON         ADMINISTRATION SYSTEMS             16
HENDERSON       OPERATIONS                         16
SCHNEIDER       OPERATIONS                         17
MEHTA           SOFTWARE SUPPORT                   16
GOUNOT          SOFTWARE SUPPORT                   16

The above examples show that the correlation name used in a subquery must be defined in the FROM clause of some query that contains the correlated subquery. However, this containment may involve several levels of nesting.

Suppose that some departments have only a few employees and therefore their average education level may be misleading. You might decide that in order for the average level of education to be a meaningful number to compare an employee against, there must be at least five employees in a department. So now we have to list the employees whose level of education is higher than the average for that employee's department, and only consider departments with at least five employees.

The problem implies another subquery because, for each employee in the outer-level query, the total number of employees in that person's department must be counted:

     SELECT COUNT(*)
        FROM EMPLOYEE E3
        WHERE E3.WORKDEPT = E1.WORKDEPT

Only if the count is greater than or equal to 5 is an average to be computed:

     SELECT AVG(EDLEVEL)
        FROM EMPLOYEE E2
        WHERE E2.WORKDEPT = E1.WORKDEPT
        AND 5 <= (SELECT COUNT(*)
                     FROM EMPLOYEE E3
                     WHERE E3.WORKDEPT = E1.WORKDEPT)

Finally, only those employees whose level of education is greater than the average for that department are included:

     SELECT LASTNAME, DEPTNAME, EDLEVEL
        FROM EMPLOYEE E1, DEPARTMENT
        WHERE E1.WORKDEPT = DEPARTMENT.DEPTNO
        AND EDLEVEL >
        (SELECT AVG(EDLEVEL)
            FROM EMPLOYEE E2
            WHERE E2.WORKDEPT = E1.WORKDEPT
            AND 5 <=
            (SELECT COUNT(*)
                FROM EMPLOYEE E3
                WHERE E3.WORKDEPT = E1.WORKDEPT))

This statement produces the following result:

     LASTNAME        DEPTNAME                      EDLEVEL
     --------------- ----------------------------- -------
     PIANKA          MANUFACTURING SYSTEMS              17
     SCOUTTEN        MANUFACTURING SYSTEMS              17
     JONES           MANUFACTURING SYSTEMS              17
     LUTZ            MANUFACTURING SYSTEMS              18
     PULASKI         ADMINISTRATION SYSTEMS             16
     MARINO          ADMINISTRATION SYSTEMS             17
     JOHNSON         ADMINISTRATION SYSTEMS             16
     HENDERSON       OPERATIONS                         16
     SCHNEIDER       OPERATIONS                         17

注：
1.什么时候用相关子查询呢�Q?br /> 当查询条件中包含有对column的函数计��时�Q�考虑使用相关子查询；
2.在Hibernate里如何实现相兛_��查询的功能呢�Q?br />

koradji 2009-11-09 14:04 发表评论

db2 PATCH用法

koradji — Wed, 04 Mar 2009 09:27:00 GMT

��试中，有时候需要��时修�?删除表中的数据，又不能媄响用��L��试。这�Ӟ��侉K��要��用PATCH来改变数据�?br /> 具体的方法是�Q�在大机环境下，�~�写shell脚本来执行db2命��o�?br /> 举例�Q?br />

#! /usr/bin/ksh
#
#
#
db2 connect to 表名 user using
db2 set current schema #导出表中数据�Q�备份检证用
db2 "export to T37A00MG_01BEFORE.csv of del messages export.log select * from T37A00MG"
db2 "export to T37A00SF_01BEFORE.csv of del messages export.log select * from T37A00SF"
#查询
db2 "select KA4ZN,TE0WA,COUNT(*) from T37A00MG group by KA4ZN,TE0WA"
db2 "select KA4ZN,TE0WA,COUNT(*) from T37A00SF group by KA4ZN,TE0WA"
#更新数据
db2 "update T37A00MG set TE0WA='SYSTEM' where TE0WA<> 'SYSTEM'"
db2 "update T37A00SF set TE0WA='SYSTEM' where TE0WA<> 'SYSTEM'"
#查询��认
db2 "select KA4ZN,TE0WA,COUNT(*) from T37A00MG group by KA4ZN,TE0WA"
db2 "select KA4ZN,TE0WA,COUNT(*) from T37A00SF group by KA4ZN,TE0WA"
#导出表中数据�Q�备份检证用
db2 "export to T37A00MG_02AFTER.csv of del messages export.log select * from T37A00MG"
db2 "export to T37A00SF_02AFTER.csv of del messages export.log select * from T37A00SF"

koradji 2009-03-04 17:27 发表评论

db2常用命��o

koradji — Wed, 04 Mar 2009 09:06:00 GMT

IBM DB2上机操作指南
1.启动实例(db2inst1)�Q�实例相当于informix中的服务
db2start
2.停止实例(db2inst1)�Q?br /> db2stop
3.列出所有实�?db2inst1)
db2ilist
4.列出当前实例�Q?br /> db2 get instance
5.察看�C�Z��配置文�g�Q?br /> db2 get dbm cfg|more
6.更新数据库管理器参数信息�Q?br /> db2 update dbm cfg using para_name para_value
7.创徏数据库：
db2 create db test
8.察看数据库配�|�参��C��?br /> db2 get db cfg for test|more
9.更新数据库参数配�|�信�?br /> db2 update db cfg for test using para_name para_value
10.删除数据库：
db2 drop db test
11.�q�接数据�?br /> db2 connect to test
12.列出所有表�I�间的详�l�信息�?br /> db2 list tablespaces show detail
13.列出容器的信�?br /> db2 list tablespace containers for tbs_id show detail
13.创徏表：
db2 ceate table tb1(id integer not null,name char(10))
14.列出所有表
db2 list tables
15.插入数据�Q?br /> db2 insert into tb1 values(1,’sam’);
db2 insert into tb2 values(2,’smitty’);
16.查询数据�Q?br /> db2 “select * from tb1”
17.删除数据�Q?br /> db2 delete from tb1 where id=1
18.创徏索引�Q?br /> db2 create index idx1 on tb1(id);
19.创徏视图�Q?br /> db2 create view view1 as select id from tb1
20.查询视图�Q?br /> db2 select * from view1
21.节点�~�目
db2 catalog tcp node node_name remote server_ip server server_port
22.察看端口�?br /> db2 get dbm cfg|grep SVCENAME
23.节点的附�?br /> db2 attach to node_name
24.察看本地节点
db2 list node direcotry
25.节点反编�?br /> db2 uncatalog node node_name
26.数据库编�?br /> db2 catalog db db_name as db_alias at node node_name
27.察看数据库的�~�目
db2 list db directory
28.�q�接数据�?br /> db2 connect to db_alias user user_name using user_password
29.数据库反�~�目
db2 uncatalog db db_alias
30.导出数据
db2 export to myfile of ixf messages msg select * from tb1
31.导入数据
db2 import from myfile of ixf messages msg replace into tb1
32.导出数据库的所有表数据
db2move test export
33.生成数据库的定义
db2look -d db_alias -a -e -m -l -x -f -o db2look.sql
34.创徏数据�?br /> db2 create db test1
35.生成定义
db2 -tvf db2look.sql
36.导入数据库所有的数据
db2move db_alias import
37.重组��?br /> db2 reorgchk
38.重组表tb1
db2 reorg table tb1
39.更新�l�计信息
db2 runstats on table tb1
40.备䆾数据库test
db2 backup db test
41.恢复数据库test
db2 restore db test
42. 拥有实例的所有程序列�?br /> db2 list application
43.
db2 terminate
44.查看数据表结�?br /> db2 “describe select * from ggwdxtcs”

/*启动命��o界面 */ db2cmd
/*查看帮助*/  db2 ? *
/*�q�接数据�?/ db2 connect to  user  using
/*查看数据库实�?/ db2ilist
/*启动数据�?/  db2start
/*停止数据库应�?/ db2 force applications all
/*停数据库*/  db2stop
/*查看表空�?  db2 list tablespaces show detail
/*查看表是否有记录*/ db2 select count(*) from
/*从文本导入到数据库表�?/ db2 import from ***.ixf of ixf modified by forcein commitcount 1000 insert into

modified by forcein  /*数据库数据在AIX �?windows 不同版本之间的格式�{�?/

commitcount **** /*防止数据库提交过多，引�v交易日志�?1000�Q?000 为宜*/
例子�Q�db2 "import from c:\zj\321104\bbsybsj.ixf of ixf modified by forcein insert into bbsybsj"
/*查看sql语句错误解释*/ db2 ? sql**** ****为四位出错编码，不��位前�?

db2 ? “sqlstate”
db2 ? sqlstate=42884
db2 “select * from syscat.functions” |grep –i rtrim
db2 “select * from syscat.indexes”
表增加列
db2 alter table 表名 add column 字段�?varchar(4)(字段�c�d��Q?br /> 修改表里的字�D?br /> db2 update 表名 set 字段�?'xxx' where .....

koradji 2009-03-04 17:06 发表评论