一、概述 对于某些需要通过数据库与大量数据打交道的软件来说，处理性能相当的重要。为了保证软件能够将所有数据处理完而不至于崩溃，分批处理的思想应运而生。分批处理的具体做法是编写SQL语句，每次返回规定条数的数据给软件处理，待这一批数据处理完之后，再接着处理下一批。 本文通过对具体的数据库表(tb_employeeinfo)的操作过程，展示了ORACLE和SYBASE数据库中分批处理SQL语句的编写方法。
二、ORACLE数据库中的处理 首先，建立tb_employeeinfo表，其定义如下：
;EXCEPTION WHEN OTHERS THEN NULL;end;/create table tb_employeeinfo(employeeno varchar2(20)not null, — no. of employeeemployeename varchar2(20)not null, — name of employeeemployeeage — age of employee);create unique index idx1_tb_employeeinfo on tb_employeeinfo(employeeno);prompt ‘create table tb_employeeinfo ok’;commit;
接着，在tb_employeeinfo表中插入7条数据，如下：
tb_employeeinfo(employeeno, employeename, employeeage) tb_employeeinfo(employeeno, employeename, employeeage) tb_employeeinfo(employeeno, employeename, employeeage) tb_employeeinfo(employeeno, employeename, employeeage) tb_employeeinfo(employeeno, employeename, employeeage) tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1006’, ‘ChenShi’, 25);
如果我们想要一次性从tb_employeeinfo表中查询出5条数据，该如何处理呢？ ORACLE数据库中有一个rownum用在查询(select)语句中来限制每次执行之后返回的数据条数。例如，本次要从tb_employeeinfo表中返回5条数据，则编写SQL语句如下：
select employeeno, employeename, employeeage from tb_employeeinfo where rownum<=5;
执行结果如下：
SQL> select employeeno, employeename, employeeage from tb_employeeinfo where rownum<=5;EMPLOYEENO EMPLOYEENAME EMPLOYEEAGEA1000ZhangSan20A1001LiSi21A1002WangWu21A1003ZhouLiu22A1004SunQi22
三、SYBASE数据库中的处理 首先，建立tb_employeeinfo表，其定义如下：
if exists(select * from sysobjects where name=’tb_employeeinfo’)drop table tb_employeeinfotb_employeeinfo(employeeno varchar(20)not null, — no. of employeeemployeename varchar(20)not null, — name of employeeemployeeage — age of employee)index idx1_tb_employeeinfo on tb_employeeinfo(employeeno)goprint ‘create table tb_employeeinfo ok’go
接着，在tb_employeeinfo表中插入7条数据，如下：
insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1000’, ‘ZhangSan’, 20)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1001’, ‘LiSi’,21)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1002’, ‘WangWu’, 21)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1003’, ‘ZhouLiu’, 22)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1004’, ‘SunQi’, 22)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1005’, ‘LiuBa’, 23)insert into tb_employeeinfo(employeeno, employeename, employeeage) values(‘A1006’, ‘ChenShi’, 25)
如果我们想要一次性从tb_employeeinfo表中查询出5条数据，该如何处理呢？ 在SYBASE数据库中，可以利用“set rowcount X”语句来实现查询条数的限制。例如，本次要从tb_employeeinfo表中返回5条数据，则编写SQL语句如下：
set rowcount 5select employeeno, employeename, employeeage from tb_employeeinfoset rowcount 0
执行结果如下：
employeenoemployeenameemployeeage A1000ZhangSan20 A1001LiSi21 A1002WangWu21 A1003ZhouLiu22 A1004SunQi22
注意，在设置了查询条数为5并查询成功之后，一定要有“set rowcount 0”语句，否则在下次执行的时候，就最多只能返回5条数据。 例如，我们先执行如下语句：
set rowcount 5select employeeno, employeename, employeeage from tb_employeeinfo
则此时返回的结果与上面一样。 再执行如下语句(本意是要将7条语句都查询出来)：
select employeeno, employeename, employeeage from tb_employeeinfo
但此时的结果仍然只返回了5条，与我们的本意不符。 因此，，在SYBASE数据库中，“set rowcount X”语句一定要与“set rowcount 0”语句配对使用。
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