LONG - такой же текстовый тип, как и VARCHAR2. НО, SQL-запрос не может содержать текстовые константы длиннее 4000 байт. По это причине лучше прислушаться к совету Oracle и перевести столбец в CLOB.
Цитата из документации "Oracle Database SQL Reference".
LONG Character data of variable length up to 2 gigabytes, or 231 -1
bytes. Provided for backward compatibility.
LONG Datatype
LONG columns store variable-length character strings containing up to 2 gigabytes -1,
or 2^31-1 bytes. LONG columns have many of the characteristics of VARCHAR2 columns.
You can use LONG columns to store long text strings. The length of LONG values may
be limited by the memory available on your computer. LONG literals are formed as
described for "Text Literals" on page 2-45.
Do not create tables with LONG columns. Use LOB columns (CLOB, NCLOB, BLOB)
instead. LONG columns are supported only for backward compatibility.
Oracle also recommends that you convert existing LONG columns to LOB columns.
LOB columns are subject to far fewer restrictions than LONG columns. Further, LOB
functionality is enhanced in every release, whereas LONG functionality has been static
for several releases. See the modify_col_properties clause of ALTER TABLE on
page 12-2 and TO_LOB on page 5-196 for more information on converting LONG
columns to LOB.
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