使用dbms_job包来实现数据库后台进程

　　1建立实现任务的过程
　　在schema manager或SQL PLUS里建立如下过程
　　CREATE OR REPLACE PROCEDURE \"CUSTOMER\".\"T_JOBTEST\" as
　　begin
　　update emp set active =0
　　where active =1
　　and date_published < sysdate - active_days;
　　end ;
　　2 向任务队列中加入任务
　　在SQL PLUS中执行下列script
　　VARIABLE jobno number;
　　begin
　　 DBMS_JOB.SUBMIT(:jobno, 't_jobtest();', SYSDATE, 'SYSDATE + 1');
　　 commit;
　　end;
　　该任务立即执行（SYSDATE），并且每隔一天执行一次（'SYSDATE + 1'）。
　　3 查询此任务是否加入任务队列
　　在SQL PLUS中执行下列script
　　SELECT job, next_date, next_sec, failures, broken
　　 FROM user_jobs;
　　------------------
　　DBMS_JOB 包介绍
　　调度任务队列里的任务要使用DBMS_JOB包中的过程。使用任务队列不需要特别的数据库特权。任何可以使用这些过程的用户都可以使用任务队列。
　　Table 8-2 DBMS_JOB包中的过程
　　Procedure Description Described

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　　SUBMIT
　　 Submits a job to the job queue. 向任务队列提交一个任务
　　REMOVE
　　 Removes a specified job from the job queue. 从任务队列中删除指定的任务
　　CHANGE
　　 Alters a specified job. You can alter the job description, the time at which the job will be run, or the interval between executions of the job. 改变任务
　　WHAT
　　 Alters the job description for a specified job. 改变指定任务的任务内容
　　NEXT_DATE
　　 Alters the next execution time for a specified job. 改变指定任务的下一次执行时间
　　INTERVAL
　　 Alters the interval between executions for a specified job. 改变指定任务的执行时间间隔。
　　BROKEN
　　 Disables job execution. If a job is marked as broken, Oracle does not attempt to execute it. 禁止指定任务的执行
　　RUN
　　 Forces a specified job to run. 强制执行指定的任务
　　Submitting a Job to the Job Queue 向任务队列提交一个任务
　　To submit a new job to the job queue, use the SUBMIT procedure in the DBMS_JOB package: 网管有家www.bitscn.net
　　DBMS_JOB.SUBMIT( job OUT BINARY_INTEGER,
　　 what IN VARCHAR2,
　　 next_date IN DATE DEFAULT SYSDATE,
　　 interval IN VARCHAR2 DEFAULT 'null',
　　 no_parse IN BOOLEAN DEFAULT FALSE)
　　The SUBMIT procedure returns the number of the job you submitted. describes the procedure's parameters.
　　Table 8-3 DBMS_JOB.SUBMIT 的参数
　　Parameter Description
　　job
　　 This is the identifier assigned to the job you created. You must use the job number whenever you want to alter or remove the job. For more information about job numbers, see \"Job Numbers\".
　　what
　　 This is the PL/SQL code you want to have executed. 这里是你想执行的PL/SQL代码
　　For more information about defining a job, see \"Job Definitions\".
　　next_date
　　 This is the next date when the job will be run. The default value is SYSDATE.
　　interval 网管u家u.bitsCN.com
　　 This is the date function that calculates the next time to execute the job. The default value is NULL. INTERVAL must evaluate to a future point in time or NULL.
　　For more information on how to specify an execution interval, see \"Job Execution Interval\".
　　no_parse
　　 This is a flag. The default value is FALSE.
　　If NO_PARSE is set to FALSE (the default), Oracle parses the procedure associated with the job. If NO_PARSE is set to TRUE, Oracle parses the procedure associated with the job the first time that the job is executed. If, for example, you want to submit a job before you have created the tables associated with the job, set NO_PARSE to TRUE.
　　As an example, let's submit a new job to the job queue. The job calls the procedure DBMS_DDL.ANALYZE_OBJECT to generate optimizer statistics for the table DQUON.ACCOUNTS. The statistics are based on a sample of half the rows of the ACCOUNTS table. The job is run every 24 hours:
　　VARIABLE jobno number;
　　begin
　　 2> DBMS_JOB.SUBMIT(:jobno, 网管u家u.bitsCN.com
　　 3> 'dbms_ddl.analyze_object(''TABLE'',
　　 4> ''DQUON'', ''ACCOUNTS'',
　　 5> ''ESTIMATE'', NULL, 50);'
　　 6> SYSDATE, 'SYSDATE + 1');
　　 7> commit;
　　 8> end;
　　 9> /
　　Statement processed.
　　print jobno
　　JOBNO
　　----------
　　14144
　　Job Definition 任务定义任务定义就是SUBMIT过程中WHAT参数中指定的PL/SQL代码。
　　通常任务定义（内容）是一个过程的一个调用。这个过程能有任意数量的参数。
　　Note: In the job definition, use two single quotation marks around strings. Always include a semicolon at the end of the job definition. 在任务定义中，用2个单引号包围字符串。任务定义的末尾总是带一个分号。
　　Jobs and Import/Export Jobs can be exported and imported.
　　 Thus, if you define a job in one database, you can transfer it to another
　　 database. When exporting and importing jobs, the job's number, environment,
　　 and definition remain unchanged.
　　任务是可以被卸出（exported ）卸入（imported）的。
　　Job Execution Interval 任务的执行间隔The INTERVAL date function is evaluated immediately before a job is executed. If the job completes successfully, the date calculated from INTERVAL becomes the new NEXT_DATE. If the INTERVAL date function evaluates to NULL and the job completes successfully, the job is
　　 deleted from the queue. If a job should be executed periodically at a set interval, use a date expression similar to 'SYSDATE + 7' in the INTERVAL
　　 parameter. For example, if you set the execution interval to 'SYSDATE + 7' on Monday, but for some reason (such as a network failure) the job is not
　　 executed until Thursday, 'SYSDATE + 7' then executes every Thursday, not Monday.
　　If you always want to automatically execute a job at a specific time, regardless of the last execution (for example, every Monday), the INTERVAL and NEXT_DATE parameters should specify a date expression similar to 'NEXT_DAY(TRUNC(SYSDATE), \"MONDAY\")'. 网管bitscn_com
　　Table 8-5 lists some common date expressions used for job execution intervals.
　　Table 8-5 Common Job Execution Intervals Date Expression Evaluation 'SYSDATE + 7'
　　 exactly seven days from the last execution 最后一次执行的7天之后执行 'SYSDATE + 1/48'
　　 every half hour 每半个小时执行一次 'NEXT_DAY(TRUNC(SYSDATE),
　　''MONDAY'') + 15/24'
　　 every Monday at 3PM 每个礼拜一的下午3点执行 'NEXT_DAY(ADD_MONTHS(TRUNC(SYSDATE, ''Q''), 3),
　　''THURSDAY'')'
　　 first Thursday of each quarter 每个季度的第一个星期四 --------------------------------------------------------------------------------Note: When specifying NEXT_DATE or INTERVAL, remember that date literals and strings must be enclosed in single quotation marks. Also, the value of INTERVAL must be enclosed in single quotation marks. --------------------------------------------------------------------------------
　　Removing a Job from the Job Queue 删除任务队列中的任务
　　To remove a job from the job queue, use the REMOVE procedure in the DBMS_JOB package: 网管u家bitscn.net
　　DBMS_JOB.REMOVE(job IN BINARY_INTEGER)
　　The following statement removes job number 14144 from the job queue:
　　DBMS_JOB.REMOVE(14144);
　　Syntax for WHAT
　　You can alter the definition of a job by calling the DBMS_JOB.WHAT procedure. Table 8-3 describes the procedure's parameters.
　　DBMS_JOB.WHAT( job IN BINARY_INTEGER,
　　 what IN VARCHAR2)
　　--------------------------------------------------------------------------------
　　Note:
　　When you execute procedure WHAT, Oracle records your current environment. This becomes