create table T1 (col_1 NVARCHAR2(2001));
ORA-00910: specified length too long for its datatype

//z 2012-08-01 13:37:33 IS2120@CSDN.T3072156621[T5,L58,R1,V32]

oracle column (field) size NVARCHAR2 大小限制
当 NLS_NCHAR_CHARACTERSET 为 AL16UTF16 的时候，最大能设置为2000
当 NLS_NCHAR_CHARACTERSET 为utf8 的时候，最大能设置为4000
这是因为NVARCHAR2数据类型，最大只能存储4000个字节。

//z 2012-08-01 13:37:33 IS2120@CSDN.T3072156621[T5,L58,R1,V32]

CHAR, NCHAR, VARCHAR2 and NVARCHAR2

Character data types store character data in the database character or national character set.

CHAR[(n [BYTE | CHAR] )]

Fixed-length character data of length n bytes or characters. The maximum length is 2000 bytes, the default value is 1.

BYTE indicates that the length semantics for the column is byte. CHAR indicates that the length semantics for the column is character. The default is BYTE. CHAR and BYTE qualifiers are not available prior to Oracle Version 9.

NCHAR[(n)]

Fixed-length character data of length n characters or bytes, depending on the national character set. The maximum length is determined by the number of bytes required to store each character, with an upper limit of 2000 bytes. The default value is 1.

VARCHAR2(n [BYTE | CHAR] )

Variable-length character data with length of n characters. The maximum length is 4000 bytes. You must specify the maximum length for VARCHAR2 columns.

BYTE indicates that the length semantics for the column is byte. CHAR indicates that the length semantics for the column is character. The default is BYTE. CHAR and BYTE qualifiers are not available prior to Oracle Version 9.

NVARCHAR2(n)

Variable-length character data having maximum length n characters or bytes, depending on the national character set. The maximum length is determined by the number of bytes required to store each character, with an upper limit of 4000 bytes. You must specify the maximum length for NVARCHAR2 columns.