这是一个带有强类型引用游标的过程：

SQL> create or replace procedure p1 is

2 type dept_rc is ref cursor return dept%rowtype;

3 my_ref_cursor dept_rc;

4 begin

5 open my_ref_cursor for

6 select * from dept;

7 end;

8 /

Procedure created.

SQL>

下一个语句失败,因为EMP记录的签名与DEPT表的签名不匹配.

SQL> create or replace procedure p1 is

2 type dept_rc is ref cursor return dept%rowtype;

3 my_ref_cursor dept_rc;

4 begin

5 open my_ref_cursor for

6 select * from emp;

7 end;

8 /

Warning: Procedure created with compilation errors.

SQL> show error

Errors for PROCEDURE P1:

LINE/COL ERROR

-------- -----------------------------------------------------------------

5/5 PL/SQL: SQL Statement ignored

6/9 PLS-00382: expression is of wrong type

SQL>

但是如果我们改变投影以匹配DEPT表,那么我们再次获得成功：

SQL> create or replace procedure p1 is

2 type dept_rc is ref cursor return dept%rowtype;

3 my_ref_cursor dept_rc;

4 begin

5 open my_ref_cursor for

6 select deptno, ename, job from emp;

7 end;

8 /

Procedure created.

SQL>

那么,为什么我们不能使用带有动态SQL的强类型引用游标？

SQL> create or replace procedure p1 is

2 type dept_rc is ref cursor return dept%rowtype;

3 my_ref_cursor dept_rc;

4 begin

5 open my_ref_cursor for

6 'select * from dept';

7 end;

8 /

Warning: Procedure created with compilation errors.

SQL> show error

Errors for PROCEDURE P1:

LINE/COL ERROR

-------- -----------------------------------------------------------------

5/5 PL/SQL: Statement ignored

5/10 PLS-00455: cursor 'MY_REF_CURSOR' cannot be used in dynamic SQL

OPEN statement

SQL>

因为编译器无法解析动态SQL语句中的字符串.因此,它无法断言查询投影中的列与数字和数据类型匹配ref游标的签名.因此,它无法验证ref游标变量和查询之间的契约.当我们考虑可以从USER_TAB_COLUMNS上的查询汇编动态SQL语句时,更容易理解为什么不允许这样做.