VARCHAR2(size [BYTE | CHAR])
Variable-length character string having maximum length size bytes or characters. You must specify size for VARCHAR2. Minimum size is 1 byte or 1 character. Maximum size is:
32767 bytes or characters if MAX_STRING_SIZE = EXTENDED
4000 bytes or characters if MAX_STRING_SIZE = STANDARD
Oracle 12C以上才支持32767字节，需要修改参数MAX_STRING_SIZE = EXTENDED