biad优秀工程设计奖:EXECUTE IMMEDIATE
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在ORACLE的PL/SQL里:
EXECUTE IMMEDIATE 代替了以前Oracle8i中DBMS_SQL package包.
它解析并马上执行动态的SQL语句或非运行时创建的PL/SQL块.动态创建和执行SQL语句性能超前,EXECUTE IMMEDIATE的目标在于减小企业费用并获得较高的性能,较之以前它相当容易编码.尽管DBMS_SQL仍然可用,但是推荐使用EXECUTE IMMEDIATE,因为它获的收益在包之上。
-- 使用技巧
1. EXECUTE IMMEDIATE将不会提交一个DML事务执行,应该显式提交
如果通过EXECUTE IMMEDIATE处理DML命令,
那么在完成以前需要显式提交或者作为EXECUTE IMMEDIATE自己的一部分.
如果通过EXECUTE IMMEDIATE处理DDL命令,它提交所有以前改变的数据
2. 不支持返回多行的查询,这种交互将用临时表来存储记录(参照例子如下)或者用REF cursors.
3. 当执行SQL语句时,不要用分号,当执行PL/SQL块时,在其尾部用分号.
4. 在Oracle手册中,未详细覆盖这些功能。
下面的例子展示了所有用到Execute immediate的可能方面.希望能给你带来方便.
5. 对于Forms开发者,当在PL/SQL 8.0.6.3.版本中,Forms 6i不能使用此功能.
EXECUTE IMMEDIATE -- 用法例子
1. 在PL/SQL运行DDL语句
- execute immediate 'set role all';
- end;
begin execute immediate 'set role all';end;
2. 给动态语句传值(USING 子句)
- declare
- l_depnam varchar2(20) := 'testing';
- l_loc varchar2(10) := 'Dubai';
- begin
- execute immediate 'insert into dept values (:1, :2, :3)'
- using 50, l_depnam, l_loc;
- commit;
- end;
declare l_depnam varchar2(20) := 'testing'; l_loc varchar2(10) := 'Dubai'; begin execute immediate 'insert into dept values (:1, :2, :3)' using 50, l_depnam, l_loc; commit;end;
Sql代码
- create or replace test(invalue in varchar2)
- is
- strsql varchar2(4000);
- begin
- strsql := 'select * from mytable where a in (:invalue)';
- execute immediate strsql using invalue;
create or replace test(invalue in varchar2) is strsql varchar2(4000); begin strsql := 'select * from mytable where a in (:invalue)'; execute immediate strsql using invalue;
3. 从动态语句检索值(INTO子句)
- l_cnt varchar2(20);
- begin
- execute immediate 'select count(1) from emp'
- into l_cnt;
- dbms_output.put_line(l_cnt);
- end;
declare l_cnt varchar2(20);begin execute immediate 'select count(1) from emp' into l_cnt; dbms_output.put_line(l_cnt);end;
4. 动态调用例程.例程中用到的绑定变量参数必须指定参数类型.
黓认为IN类型,其它类型必须显式指定
- l_routin varchar2(100) := 'gen2161.get_rowcnt';
- l_tblnam varchar2(20) := 'emp';
- l_cnt number;
- l_status varchar2(200);
- begin
- execute immediate 'begin ' || l_routin || '(:2, :3, :4); end;'
- using in l_tblnam, out l_cnt, in out l_status;
- if l_status != 'OK' then
- dbms_output.put_line('error');
- end if;
- end;
declare l_routin varchar2(100) := 'gen2161.get_rowcnt'; l_tblnam varchar2(20) := 'emp'; l_cnt number; l_status varchar2(200);begin execute immediate 'begin ' || l_routin || '(:2, :3, :4); end;' using in l_tblnam, out l_cnt, in out l_status; if l_status != 'OK' then dbms_output.put_line('error'); end if;end;
5. 将返回值传递到PL/SQL记录类型;同样也可用%rowtype变量
- type empdtlrec is record (empno number(4),
- ename varchar2(20),
- deptno number(2));
- empdtl empdtlrec;
- begin
- execute immediate 'select empno, ename, deptno ' ||
- 'from emp where empno = 7934'
- into empdtl;
- end;
declare type empdtlrec is record (empno number(4), ename varchar2(20), deptno number(2)); empdtl empdtlrec;begin execute immediate 'select empno, ename, deptno ' || 'from emp where empno = 7934' into empdtl;end;
6. 传递并检索值.INTO子句用在USING子句前
- l_dept pls_integer := 20;
- l_nam varchar2(20);
- l_loc varchar2(20);
- begin
- execute immediate 'select dname, loc from dept where deptno = :1'
- into l_nam, l_loc
- using l_dept ;
- end;
declare l_dept pls_integer := 20; l_nam varchar2(20); l_loc varchar2(20);begin execute immediate 'select dname, loc from dept where deptno = :1' into l_nam, l_loc using l_dept ;end;
7. 多行查询选项.对此选项用insert语句填充临时表,
用临时表进行进一步的处理,也可以用REF cursors纠正此缺憾.
- declare
- l_sal pls_integer := 2000;
- begin
- execute immediate 'insert into temp(empno, ename) ' ||
- ' select empno, ename from emp ' ||
- ' where sal > :1'
- using l_sal;
- commit;
- end;
declare l_sal pls_integer := 2000;begin execute immediate 'insert into temp(empno, ename) ' || ' select empno, ename from emp ' || ' where sal > :1' using l_sal; commit;end;
对于处理动态语句,EXECUTE IMMEDIATE 比以前可能用到的更容易并且更高效.
当意图执行动态语句时,适当地处理异常更加重要.应该关注于捕获所有可能的异常.