表中的LONG列可以存储文本，字符数组，甚至短文档。可以针对该类型列做UPDATE, INSERT, 和SELECT 操作。
但是无法再表达式，SQL函数调用或特定的SQL条件语句例如WHERE, GROUP BY和CONNECT BY。
In SQL statements, PL/SQL binds LONG values as VARCHAR2, not as LONG. However,
if the length of the bound VARCHAR2 exceeds the maximum width of a VARCHAR2
column (4000 bytes), Oracle converts the bind type to LONG automatically, then issues
an error message because you cannot pass LONG values to a SQL function
SQL语句中， PL/SQL将LONG类型作为VARCHAR2类型绑定。然而，如果所绑定的VARCHAR2长度超出了4000，ORACLE会自动转换到LONG，
然后抛出一个错误因为你不能将LONG值传递给SQL函数。
--例如：
SCOTT@orcl> create table long_test(id number, msg long);
表已创建。
SCOTT@orcl> insert into long_test values(1,'hello world');
已创建 1 行。
SCOTT@orcl> commit;
提交完成。
SCOTT@orcl> select * from long_test where msg='123';
select * from long_test where msg='123'
*
第 1 行出现错误:
ORA-00997: 非法使用 LONG 数据类型
SCOTT@orcl> /
ID MSG
---------- --------------------------------------------------------------------------------
1 hello world
SCOTT@orcl> select id, trim(msg) from long_test where id = 1;
select id, trim(msg) from long_test where id = 1
*
第 1 行出现错误:
ORA-00932: 数据类型不一致: 应为 NUMBER, 但却获得 LONG3、CLOB
可以使用CLOB类型大块的字符数据。每一个CLOB变量存储一个定位器，指向一个大块字符数据。
CLOBs participate fully in transactions, are recoverable, and can be replicated. Changes
made by package DBMS_LOB can be committed or rolled back. CLOB locators can span
transactions (for reads only), but they cannot span sessions.
CLOB参与整体事务，可恢复，并且可以重复。
由DBMS_LOB包改变的数据可以提交和回滚。CLOB定位器可以跨事务，但不能跨会话。
4、BLOB
You use the BLOB datatype to store large binary objects in the database, in-line or
out-of-line. Every BLOB variable stores a locator, which points to a large binary object.
BLOBs participate fully in transactions, are recoverable, and can be replicated. Changes
made by package DBMS_LOB can be committed or rolled back. BLOB locators can span
transactions (for reads only), but they cannot span sessions.
用于存储大二进制对象，BLOB参与整体事务，可恢复，并且可以重复。
由DBMS_LOB包改变的数据可以提交和回滚。BLOB定位器可以跨事务，但不能跨会话。
drop table blob_test;
SCOTT@orcl> create table blob_test( id number primary key, content blob not null);
表已创建。
SCOTT@orcl> insert into blob_test values(1,'11111000011111');
已创建 1 行。
SCOTT@orcl> commit;
提交完成。
SCOTT@orcl> select * from blob_test;
SCOTT@orcl> set linesize 2000
SCOTT@orcl> /
ID CONTENT
---------- -----------------------------------
1 11111000011111
SCOTT@orcl> insert into blob_test values(1,'11111000011111>');
insert into blob_test values(1,'11111000011111>')
*
第 1 行出现错误:
ORA-01465: 无效的十六进制数字
SCOTT@orcl> update blob_test set content=to_blob('110010000110011') where id=1;
已更新 1 行。
SCOTT@orcl> rollback
2 ;
回退已完成。
SCOTT@orcl> select * from blob_test;
ID CONTENT
---------- ---------------------------------------------------------------------
1 11111000011111
delete from blob_test where id=1;
commit;