方法1：set serveroutput on size 10000000 //设置大点,默认为2000 bytes
方法2：exec dbms_output.enable(999999999999999999999); //设置大点,默认为2000 bytes
出现这个错误的原因是因为dbms_output缓冲区的溢出。具体如下：
The DBMS_OUTPUT package enables you to send messages from stored procedures, packages, and triggers.
The PUT and PUT_LINE procedures in this package enable you to place information in a buffer that can be read by another trigger, procedure, or package. In a separate PL/SQL procedure or anonymous block, you can display the buffered information by calling the
GET_LINE procedure.
这个包提供了这个缓冲区，但是这个缓冲区大小是有限制的,像上面的两个方法那样设置大小，问题就可以解决。