LONG[VARCHAR] 
The LONG [VARCHAR] data type is used to define an alphanumeric column of any length (not for temporary tables). The LONG data type (see also: Glossary, LONG Value) is specified in the column definition, with a code attribute, if necessary.
● LONG [VARCHAR] [ASCII | BYTE]: A maximum of 2 GB of characters can be written in a LONG column.
● LONG[VARCHAR] UNICODE: A maximum of 2 GB bytes can be written in a LONG column.
Explanation
You can only use a few functions on a LONG column: DECODE, LENGTH and SUBSTR.
LONG columns cannot be compared to one another. The contents of LONG columns cannot be compared to character strings or other data types.
LONG columns can only contain as a column attribute NOT NULL or a DEFAULT specification.
LONG columns can be used in the following SQL statements and syntax elements: